Merge crate `collections` into `alloc`

1 files changed, 1236 insertions, 0 deletions

diff --git a/src/liballoc/binary_heap.rs b/src/liballoc/binary_heap.rs
new file mode 100644
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+// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! A priority queue implemented with a binary heap.
+//!
+//! Insertion and popping the largest element have `O(log n)` time complexity.
+//! Checking the largest element is `O(1)`. Converting a vector to a binary heap
+//! can be done in-place, and has `O(n)` complexity. A binary heap can also be
+//! converted to a sorted vector in-place, allowing it to be used for an `O(n
+//! log n)` in-place heapsort.
+//!
+//! # Examples
+//!
+//! This is a larger example that implements [Dijkstra's algorithm][dijkstra]
+//! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph].
+//! It shows how to use [`BinaryHeap`] with custom types.
+//!
+//! [dijkstra]: http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
+//! [sssp]: http://en.wikipedia.org/wiki/Shortest_path_problem
+//! [dir_graph]: http://en.wikipedia.org/wiki/Directed_graph
+//! [`BinaryHeap`]: struct.BinaryHeap.html
+//!
+//! ```
+//! use std::cmp::Ordering;
+//! use std::collections::BinaryHeap;
+//! use std::usize;
+//!
+//! #[derive(Copy, Clone, Eq, PartialEq)]
+//! struct State {
+//!     cost: usize,
+//!     position: usize,
+//! }
+//!
+//! // The priority queue depends on `Ord`.
+//! // Explicitly implement the trait so the queue becomes a min-heap
+//! // instead of a max-heap.
+//! impl Ord for State {
+//!     fn cmp(&self, other: &State) -> Ordering {
+//!         // Notice that the we flip the ordering on costs.
+//!         // In case of a tie we compare positions - this step is necessary
+//!         // to make implementations of `PartialEq` and `Ord` consistent.
+//!         other.cost.cmp(&self.cost)
+//!             .then_with(|| self.position.cmp(&other.position))
+//!     }
+//! }
+//!
+//! // `PartialOrd` needs to be implemented as well.
+//! impl PartialOrd for State {
+//!     fn partial_cmp(&self, other: &State) -> Option<Ordering> {
+//!         Some(self.cmp(other))
+//!     }
+//! }
+//!
+//! // Each node is represented as an `usize`, for a shorter implementation.
+//! struct Edge {
+//!     node: usize,
+//!     cost: usize,
+//! }
+//!
+//! // Dijkstra's shortest path algorithm.
+//!
+//! // Start at `start` and use `dist` to track the current shortest distance
+//! // to each node. This implementation isn't memory-efficient as it may leave duplicate
+//! // nodes in the queue. It also uses `usize::MAX` as a sentinel value,
+//! // for a simpler implementation.
+//! fn shortest_path(adj_list: &Vec<Vec<Edge>>, start: usize, goal: usize) -> Option<usize> {
+//!     // dist[node] = current shortest distance from `start` to `node`
+//!     let mut dist: Vec<_> = (0..adj_list.len()).map(|_| usize::MAX).collect();
+//!
+//!     let mut heap = BinaryHeap::new();
+//!
+//!     // We're at `start`, with a zero cost
+//!     dist[start] = 0;
+//!     heap.push(State { cost: 0, position: start });
+//!
+//!     // Examine the frontier with lower cost nodes first (min-heap)
+//!     while let Some(State { cost, position }) = heap.pop() {
+//!         // Alternatively we could have continued to find all shortest paths
+//!         if position == goal { return Some(cost); }
+//!
+//!         // Important as we may have already found a better way
+//!         if cost > dist[position] { continue; }
+//!
+//!         // For each node we can reach, see if we can find a way with
+//!         // a lower cost going through this node
+//!         for edge in &adj_list[position] {
+//!             let next = State { cost: cost + edge.cost, position: edge.node };
+//!
+//!             // If so, add it to the frontier and continue
+//!             if next.cost < dist[next.position] {
+//!                 heap.push(next);
+//!                 // Relaxation, we have now found a better way
+//!                 dist[next.position] = next.cost;
+//!             }
+//!         }
+//!     }
+//!
+//!     // Goal not reachable
+//!     None
+//! }
+//!
+//! fn main() {
+//!     // This is the directed graph we're going to use.
+//!     // The node numbers correspond to the different states,
+//!     // and the edge weights symbolize the cost of moving
+//!     // from one node to another.
+//!     // Note that the edges are one-way.
+//!     //
+//!     //                  7
+//!     //          +-----------------+
+//!     //          |                 |
+//!     //          v   1        2    |  2
+//!     //          0 -----> 1 -----> 3 ---> 4
+//!     //          |        ^        ^      ^
+//!     //          |        | 1      |      |
+//!     //          |        |        | 3    | 1
+//!     //          +------> 2 -------+      |
+//!     //           10      |               |
+//!     //                   +---------------+
+//!     //
+//!     // The graph is represented as an adjacency list where each index,
+//!     // corresponding to a node value, has a list of outgoing edges.
+//!     // Chosen for its efficiency.
+//!     let graph = vec![
+//!         // Node 0
+//!         vec![Edge { node: 2, cost: 10 },
+//!              Edge { node: 1, cost: 1 }],
+//!         // Node 1
+//!         vec![Edge { node: 3, cost: 2 }],
+//!         // Node 2
+//!         vec![Edge { node: 1, cost: 1 },
+//!              Edge { node: 3, cost: 3 },
+//!              Edge { node: 4, cost: 1 }],
+//!         // Node 3
+//!         vec![Edge { node: 0, cost: 7 },
+//!              Edge { node: 4, cost: 2 }],
+//!         // Node 4
+//!         vec![]];
+//!
+//!     assert_eq!(shortest_path(&graph, 0, 1), Some(1));
+//!     assert_eq!(shortest_path(&graph, 0, 3), Some(3));
+//!     assert_eq!(shortest_path(&graph, 3, 0), Some(7));
+//!     assert_eq!(shortest_path(&graph, 0, 4), Some(5));
+//!     assert_eq!(shortest_path(&graph, 4, 0), None);
+//! }
+//! ```
+
+#![allow(missing_docs)]
+#![stable(feature = "rust1", since = "1.0.0")]
+
+use core::ops::{Deref, DerefMut, Place, Placer, InPlace};
+use core::iter::{FromIterator, FusedIterator};
+use core::mem::{swap, size_of};
+use core::ptr;
+use core::fmt;
+
+use slice;
+use vec::{self, Vec};
+
+use super::SpecExtend;
+
+/// A priority queue implemented with a binary heap.
+///
+/// This will be a max-heap.
+///
+/// It is a logic error for an item to be modified in such a way that the
+/// item's ordering relative to any other item, as determined by the `Ord`
+/// trait, changes while it is in the heap. This is normally only possible
+/// through `Cell`, `RefCell`, global state, I/O, or unsafe code.
+///
+/// # Examples
+///
+/// ```
+/// use std::collections::BinaryHeap;
+///
+/// // Type inference lets us omit an explicit type signature (which
+/// // would be `BinaryHeap<i32>` in this example).
+/// let mut heap = BinaryHeap::new();
+///
+/// // We can use peek to look at the next item in the heap. In this case,
+/// // there's no items in there yet so we get None.
+/// assert_eq!(heap.peek(), None);
+///
+/// // Let's add some scores...
+/// heap.push(1);
+/// heap.push(5);
+/// heap.push(2);
+///
+/// // Now peek shows the most important item in the heap.
+/// assert_eq!(heap.peek(), Some(&5));
+///
+/// // We can check the length of a heap.
+/// assert_eq!(heap.len(), 3);
+///
+/// // We can iterate over the items in the heap, although they are returned in
+/// // a random order.
+/// for x in &heap {
+///     println!("{}", x);
+/// }
+///
+/// // If we instead pop these scores, they should come back in order.
+/// assert_eq!(heap.pop(), Some(5));
+/// assert_eq!(heap.pop(), Some(2));
+/// assert_eq!(heap.pop(), Some(1));
+/// assert_eq!(heap.pop(), None);
+///
+/// // We can clear the heap of any remaining items.
+/// heap.clear();
+///
+/// // The heap should now be empty.
+/// assert!(heap.is_empty())
+/// ```
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct BinaryHeap<T> {
+    data: Vec<T>,
+}
+
+/// Structure wrapping a mutable reference to the greatest item on a
+/// `BinaryHeap`.
+///
+/// This `struct` is created by the [`peek_mut`] method on [`BinaryHeap`]. See
+/// its documentation for more.
+///
+/// [`peek_mut`]: struct.BinaryHeap.html#method.peek_mut
+/// [`BinaryHeap`]: struct.BinaryHeap.html
+#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
+pub struct PeekMut<'a, T: 'a + Ord> {
+    heap: &'a mut BinaryHeap<T>,
+    sift: bool,
+}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<'a, T: Ord + fmt::Debug> fmt::Debug for PeekMut<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("PeekMut")
+         .field(&self.heap.data[0])
+         .finish()
+    }
+}
+
+#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
+impl<'a, T: Ord> Drop for PeekMut<'a, T> {
+    fn drop(&mut self) {
+        if self.sift {
+            self.heap.sift_down(0);
+        }
+    }
+}
+
+#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
+impl<'a, T: Ord> Deref for PeekMut<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        &self.heap.data[0]
+    }
+}
+
+#[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
+impl<'a, T: Ord> DerefMut for PeekMut<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.heap.data[0]
+    }
+}
+
+impl<'a, T: Ord> PeekMut<'a, T> {
+    /// Removes the peeked value from the heap and returns it.
+    #[stable(feature = "binary_heap_peek_mut_pop", since = "1.18.0")]
+    pub fn pop(mut this: PeekMut<'a, T>) -> T {
+        let value = this.heap.pop().unwrap();
+        this.sift = false;
+        value
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Clone> Clone for BinaryHeap<T> {
+    fn clone(&self) -> Self {
+        BinaryHeap { data: self.data.clone() }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.data.clone_from(&source.data);
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> Default for BinaryHeap<T> {
+    /// Creates an empty `BinaryHeap<T>`.
+    #[inline]
+    fn default() -> BinaryHeap<T> {
+        BinaryHeap::new()
+    }
+}
+
+#[stable(feature = "binaryheap_debug", since = "1.4.0")]
+impl<T: fmt::Debug + Ord> fmt::Debug for BinaryHeap<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<T: Ord> BinaryHeap<T> {
+    /// Creates an empty `BinaryHeap` as a max-heap.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// heap.push(4);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn new() -> BinaryHeap<T> {
+        BinaryHeap { data: vec![] }
+    }
+
+    /// Creates an empty `BinaryHeap` with a specific capacity.
+    /// This preallocates enough memory for `capacity` elements,
+    /// so that the `BinaryHeap` does not have to be reallocated
+    /// until it contains at least that many values.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::with_capacity(10);
+    /// heap.push(4);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn with_capacity(capacity: usize) -> BinaryHeap<T> {
+        BinaryHeap { data: Vec::with_capacity(capacity) }
+    }
+
+    /// Returns an iterator visiting all values in the underlying vector, in
+    /// arbitrary order.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let heap = BinaryHeap::from(vec![1, 2, 3, 4]);
+    ///
+    /// // Print 1, 2, 3, 4 in arbitrary order
+    /// for x in heap.iter() {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn iter(&self) -> Iter<T> {
+        Iter { iter: self.data.iter() }
+    }
+
+    /// Returns the greatest item in the binary heap, or `None` if it is empty.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// assert_eq!(heap.peek(), None);
+    ///
+    /// heap.push(1);
+    /// heap.push(5);
+    /// heap.push(2);
+    /// assert_eq!(heap.peek(), Some(&5));
+    ///
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn peek(&self) -> Option<&T> {
+        self.data.get(0)
+    }
+
+    /// Returns a mutable reference to the greatest item in the binary heap, or
+    /// `None` if it is empty.
+    ///
+    /// Note: If the `PeekMut` value is leaked, the heap may be in an
+    /// inconsistent state.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// assert!(heap.peek_mut().is_none());
+    ///
+    /// heap.push(1);
+    /// heap.push(5);
+    /// heap.push(2);
+    /// {
+    ///     let mut val = heap.peek_mut().unwrap();
+    ///     *val = 0;
+    /// }
+    /// assert_eq!(heap.peek(), Some(&2));
+    /// ```
+    #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
+    pub fn peek_mut(&mut self) -> Option<PeekMut<T>> {
+        if self.is_empty() {
+            None
+        } else {
+            Some(PeekMut {
+                heap: self,
+                sift: true,
+            })
+        }
+    }
+
+    /// Returns the number of elements the binary heap can hold without reallocating.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::with_capacity(100);
+    /// assert!(heap.capacity() >= 100);
+    /// heap.push(4);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn capacity(&self) -> usize {
+        self.data.capacity()
+    }
+
+    /// Reserves the minimum capacity for exactly `additional` more elements to be inserted in the
+    /// given `BinaryHeap`. Does nothing if the capacity is already sufficient.
+    ///
+    /// Note that the allocator may give the collection more space than it requests. Therefore
+    /// capacity can not be relied upon to be precisely minimal. Prefer [`reserve`] if future
+    /// insertions are expected.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// heap.reserve_exact(100);
+    /// assert!(heap.capacity() >= 100);
+    /// heap.push(4);
+    /// ```
+    ///
+    /// [`reserve`]: #method.reserve
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve_exact(&mut self, additional: usize) {
+        self.data.reserve_exact(additional);
+    }
+
+    /// Reserves capacity for at least `additional` more elements to be inserted in the
+    /// `BinaryHeap`. The collection may reserve more space to avoid frequent reallocations.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new capacity overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// heap.reserve(100);
+    /// assert!(heap.capacity() >= 100);
+    /// heap.push(4);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn reserve(&mut self, additional: usize) {
+        self.data.reserve(additional);
+    }
+
+    /// Discards as much additional capacity as possible.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap: BinaryHeap<i32> = BinaryHeap::with_capacity(100);
+    ///
+    /// assert!(heap.capacity() >= 100);
+    /// heap.shrink_to_fit();
+    /// assert!(heap.capacity() == 0);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn shrink_to_fit(&mut self) {
+        self.data.shrink_to_fit();
+    }
+
+    /// Removes the greatest item from the binary heap and returns it, or `None` if it
+    /// is empty.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::from(vec![1, 3]);
+    ///
+    /// assert_eq!(heap.pop(), Some(3));
+    /// assert_eq!(heap.pop(), Some(1));
+    /// assert_eq!(heap.pop(), None);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn pop(&mut self) -> Option<T> {
+        self.data.pop().map(|mut item| {
+            if !self.is_empty() {
+                swap(&mut item, &mut self.data[0]);
+                self.sift_down_to_bottom(0);
+            }
+            item
+        })
+    }
+
+    /// Pushes an item onto the binary heap.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    /// heap.push(3);
+    /// heap.push(5);
+    /// heap.push(1);
+    ///
+    /// assert_eq!(heap.len(), 3);
+    /// assert_eq!(heap.peek(), Some(&5));
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn push(&mut self, item: T) {
+        let old_len = self.len();
+        self.data.push(item);
+        self.sift_up(0, old_len);
+    }
+
+    /// Consumes the `BinaryHeap` and returns the underlying vector
+    /// in arbitrary order.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let heap = BinaryHeap::from(vec![1, 2, 3, 4, 5, 6, 7]);
+    /// let vec = heap.into_vec();
+    ///
+    /// // Will print in some order
+    /// for x in vec {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
+    pub fn into_vec(self) -> Vec<T> {
+        self.into()
+    }
+
+    /// Consumes the `BinaryHeap` and returns a vector in sorted
+    /// (ascending) order.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    ///
+    /// let mut heap = BinaryHeap::from(vec![1, 2, 4, 5, 7]);
+    /// heap.push(6);
+    /// heap.push(3);
+    ///
+    /// let vec = heap.into_sorted_vec();
+    /// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
+    /// ```
+    #[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
+    pub fn into_sorted_vec(mut self) -> Vec<T> {
+        let mut end = self.len();
+        while end > 1 {
+            end -= 1;
+            self.data.swap(0, end);
+            self.sift_down_range(0, end);
+        }
+        self.into_vec()
+    }
+
+    // The implementations of sift_up and sift_down use unsafe blocks in
+    // order to move an element out of the vector (leaving behind a
+    // hole), shift along the others and move the removed element back into the
+    // vector at the final location of the hole.
+    // The `Hole` type is used to represent this, and make sure
+    // the hole is filled back at the end of its scope, even on panic.
+    // Using a hole reduces the constant factor compared to using swaps,
+    // which involves twice as many moves.
+    fn sift_up(&mut self, start: usize, pos: usize) -> usize {
+        unsafe {
+            // Take out the value at `pos` and create a hole.
+            let mut hole = Hole::new(&mut self.data, pos);
+
+            while hole.pos() > start {
+                let parent = (hole.pos() - 1) / 2;
+                if hole.element() <= hole.get(parent) {
+                    break;
+                }
+                hole.move_to(parent);
+            }
+            hole.pos()
+        }
+    }
+
+    /// Take an element at `pos` and move it down the heap,
+    /// while its children are larger.
+    fn sift_down_range(&mut self, pos: usize, end: usize) {
+        unsafe {
+            let mut hole = Hole::new(&mut self.data, pos);
+            let mut child = 2 * pos + 1;
+            while child < end {
+                let right = child + 1;
+                // compare with the greater of the two children
+                if right < end && !(hole.get(child) > hole.get(right)) {
+                    child = right;
+                }
+                // if we are already in order, stop.
+                if hole.element() >= hole.get(child) {
+                    break;
+                }
+                hole.move_to(child);
+                child = 2 * hole.pos() + 1;
+            }
+        }
+    }
+
+    fn sift_down(&mut self, pos: usize) {
+        let len = self.len();
+        self.sift_down_range(pos, len);
+    }
+
+    /// Take an element at `pos` and move it all the way down the heap,
+    /// then sift it up to its position.
+    ///
+    /// Note: This is faster when the element is known to be large / should
+    /// be closer to the bottom.
+    fn sift_down_to_bottom(&mut self, mut pos: usize) {
+        let end = self.len();
+        let start = pos;
+        unsafe {
+            let mut hole = Hole::new(&mut self.data, pos);
+            let mut child = 2 * pos + 1;
+            while child < end {
+                let right = child + 1;
+                // compare with the greater of the two children
+                if right < end && !(hole.get(child) > hole.get(right)) {
+                    child = right;
+                }
+                hole.move_to(child);
+                child = 2 * hole.pos() + 1;
+            }
+            pos = hole.pos;
+        }
+        self.sift_up(start, pos);
+    }
+
+    /// Returns the length of the binary heap.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let heap = BinaryHeap::from(vec![1, 3]);
+    ///
+    /// assert_eq!(heap.len(), 2);
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn len(&self) -> usize {
+        self.data.len()
+    }
+
+    /// Checks if the binary heap is empty.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::new();
+    ///
+    /// assert!(heap.is_empty());
+    ///
+    /// heap.push(3);
+    /// heap.push(5);
+    /// heap.push(1);
+    ///
+    /// assert!(!heap.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Clears the binary heap, returning an iterator over the removed elements.
+    ///
+    /// The elements are removed in arbitrary order.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::from(vec![1, 3]);
+    ///
+    /// assert!(!heap.is_empty());
+    ///
+    /// for x in heap.drain() {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// assert!(heap.is_empty());
+    /// ```
+    #[inline]
+    #[stable(feature = "drain", since = "1.6.0")]
+    pub fn drain(&mut self) -> Drain<T> {
+        Drain { iter: self.data.drain(..) }
+    }
+
+    /// Drops all items from the binary heap.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let mut heap = BinaryHeap::from(vec![1, 3]);
+    ///
+    /// assert!(!heap.is_empty());
+    ///
+    /// heap.clear();
+    ///
+    /// assert!(heap.is_empty());
+    /// ```
+    #[stable(feature = "rust1", since = "1.0.0")]
+    pub fn clear(&mut self) {
+        self.drain();
+    }
+
+    fn rebuild(&mut self) {
+        let mut n = self.len() / 2;
+        while n > 0 {
+            n -= 1;
+            self.sift_down(n);
+        }
+    }
+
+    /// Moves all the elements of `other` into `self`, leaving `other` empty.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    ///
+    /// let v = vec![-10, 1, 2, 3, 3];
+    /// let mut a = BinaryHeap::from(v);
+    ///
+    /// let v = vec![-20, 5, 43];
+    /// let mut b = BinaryHeap::from(v);
+    ///
+    /// a.append(&mut b);
+    ///
+    /// assert_eq!(a.into_sorted_vec(), [-20, -10, 1, 2, 3, 3, 5, 43]);
+    /// assert!(b.is_empty());
+    /// ```
+    #[stable(feature = "binary_heap_append", since = "1.11.0")]
+    pub fn append(&mut self, other: &mut Self) {
+        if self.len() < other.len() {
+            swap(self, other);
+        }
+
+        if other.is_empty() {
+            return;
+        }
+
+        #[inline(always)]
+        fn log2_fast(x: usize) -> usize {
+            8 * size_of::<usize>() - (x.leading_zeros() as usize) - 1
+        }
+
+        // `rebuild` takes O(len1 + len2) operations
+        // and about 2 * (len1 + len2) comparisons in the worst case
+        // while `extend` takes O(len2 * log_2(len1)) operations
+        // and about 1 * len2 * log_2(len1) comparisons in the worst case,
+        // assuming len1 >= len2.
+        #[inline]
+        fn better_to_rebuild(len1: usize, len2: usize) -> bool {
+            2 * (len1 + len2) < len2 * log2_fast(len1)
+        }
+
+        if better_to_rebuild(self.len(), other.len()) {
+            self.data.append(&mut other.data);
+            self.rebuild();
+        } else {
+            self.extend(other.drain());
+        }
+    }
+}
+
+/// Hole represents a hole in a slice i.e. an index without valid value
+/// (because it was moved from or duplicated).
+/// In drop, `Hole` will restore the slice by filling the hole
+/// position with the value that was originally removed.
+struct Hole<'a, T: 'a> {
+    data: &'a mut [T],
+    /// `elt` is always `Some` from new until drop.
+    elt: Option<T>,
+    pos: usize,
+}
+
+impl<'a, T> Hole<'a, T> {
+    /// Create a new Hole at index `pos`.
+    ///
+    /// Unsafe because pos must be within the data slice.
+    #[inline]
+    unsafe fn new(data: &'a mut [T], pos: usize) -> Self {
+        debug_assert!(pos < data.len());
+        let elt = ptr::read(&data[pos]);
+        Hole {
+            data: data,
+            elt: Some(elt),
+            pos: pos,
+        }
+    }
+
+    #[inline]
+    fn pos(&self) -> usize {
+        self.pos
+    }
+
+    /// Returns a reference to the element removed.
+    #[inline]
+    fn element(&self) -> &T {
+        self.elt.as_ref().unwrap()
+    }
+
+    /// Returns a reference to the element at `index`.
+    ///
+    /// Unsafe because index must be within the data slice and not equal to pos.
+    #[inline]
+    unsafe fn get(&self, index: usize) -> &T {
+        debug_assert!(index != self.pos);
+        debug_assert!(index < self.data.len());
+        self.data.get_unchecked(index)
+    }
+
+    /// Move hole to new location
+    ///
+    /// Unsafe because index must be within the data slice and not equal to pos.
+    #[inline]
+    unsafe fn move_to(&mut self, index: usize) {
+        debug_assert!(index != self.pos);
+        debug_assert!(index < self.data.len());
+        let index_ptr: *const _ = self.data.get_unchecked(index);
+        let hole_ptr = self.data.get_unchecked_mut(self.pos);
+        ptr::copy_nonoverlapping(index_ptr, hole_ptr, 1);
+        self.pos = index;
+    }
+}
+
+impl<'a, T> Drop for Hole<'a, T> {
+    #[inline]
+    fn drop(&mut self) {
+        // fill the hole again
+        unsafe {
+            let pos = self.pos;
+            ptr::write(self.data.get_unchecked_mut(pos), self.elt.take().unwrap());
+        }
+    }
+}
+
+/// An iterator over the elements of a `BinaryHeap`.
+///
+/// This `struct` is created by the [`iter`] method on [`BinaryHeap`]. See its
+/// documentation for more.
+///
+/// [`iter`]: struct.BinaryHeap.html#method.iter
+/// [`BinaryHeap`]: struct.BinaryHeap.html
+#[stable(feature = "rust1", since = "1.0.0")]
+pub struct Iter<'a, T: 'a> {
+    iter: slice::Iter<'a, T>,
+}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<'a, T: 'a + fmt::Debug> fmt::Debug for Iter<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("Iter")
+         .field(&self.iter.as_slice())
+         .finish()
+    }
+}
+
+// FIXME(#19839) Remove in favor of `#[derive(Clone)]`
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Clone for Iter<'a, T> {
+    fn clone(&self) -> Iter<'a, T> {
+        Iter { iter: self.iter.clone() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    #[inline]
+    fn next(&mut self) -> Option<&'a T> {
+        self.iter.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<&'a T> {
+        self.iter.next_back()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> ExactSizeIterator for Iter<'a, T> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Iter<'a, T> {}
+
+/// An owning iterator over the elements of a `BinaryHeap`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`BinaryHeap`][`BinaryHeap`]
+/// (provided by the `IntoIterator` trait). See its documentation for more.
+///
+/// [`into_iter`]: struct.BinaryHeap.html#method.into_iter
+/// [`BinaryHeap`]: struct.BinaryHeap.html
+#[stable(feature = "rust1", since = "1.0.0")]
+#[derive(Clone)]
+pub struct IntoIter<T> {
+    iter: vec::IntoIter<T>,
+}
+
+#[stable(feature = "collection_debug", since = "1.17.0")]
+impl<T: fmt::Debug> fmt::Debug for IntoIter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("IntoIter")
+         .field(&self.iter.as_slice())
+         .finish()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        self.iter.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        self.iter.next_back()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> ExactSizeIterator for IntoIter<T> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
+
+/// A draining iterator over the elements of a `BinaryHeap`.
+///
+/// This `struct` is created by the [`drain`] method on [`BinaryHeap`]. See its
+/// documentation for more.
+///
+/// [`drain`]: struct.BinaryHeap.html#method.drain
+/// [`BinaryHeap`]: struct.BinaryHeap.html
+#[stable(feature = "drain", since = "1.6.0")]
+#[derive(Debug)]
+pub struct Drain<'a, T: 'a> {
+    iter: vec::Drain<'a, T>,
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T: 'a> Iterator for Drain<'a, T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<T> {
+        self.iter.next()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T: 'a> DoubleEndedIterator for Drain<'a, T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<T> {
+        self.iter.next_back()
+    }
+}
+
+#[stable(feature = "drain", since = "1.6.0")]
+impl<'a, T: 'a> ExactSizeIterator for Drain<'a, T> {
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
+}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: 'a> FusedIterator for Drain<'a, T> {}
+
+#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
+impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
+    fn from(vec: Vec<T>) -> BinaryHeap<T> {
+        let mut heap = BinaryHeap { data: vec };
+        heap.rebuild();
+        heap
+    }
+}
+
+#[stable(feature = "binary_heap_extras_15", since = "1.5.0")]
+impl<T> From<BinaryHeap<T>> for Vec<T> {
+    fn from(heap: BinaryHeap<T>) -> Vec<T> {
+        heap.data
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> FromIterator<T> for BinaryHeap<T> {
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> BinaryHeap<T> {
+        BinaryHeap::from(iter.into_iter().collect::<Vec<_>>())
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> IntoIterator for BinaryHeap<T> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out of
+    /// the binary heap in arbitrary order. The binary heap cannot be used
+    /// after calling this.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use std::collections::BinaryHeap;
+    /// let heap = BinaryHeap::from(vec![1, 2, 3, 4]);
+    ///
+    /// // Print 1, 2, 3, 4 in arbitrary order
+    /// for x in heap.into_iter() {
+    ///     // x has type i32, not &i32
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    fn into_iter(self) -> IntoIter<T> {
+        IntoIter { iter: self.data.into_iter() }
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T> IntoIterator for &'a BinaryHeap<T>
+    where T: Ord
+{
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T: Ord> Extend<T> for BinaryHeap<T> {
+    #[inline]
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        <Self as SpecExtend<I>>::spec_extend(self, iter);
+    }
+}
+
+impl<T: Ord, I: IntoIterator<Item = T>> SpecExtend<I> for BinaryHeap<T> {
+    default fn spec_extend(&mut self, iter: I) {
+        self.extend_desugared(iter.into_iter());
+    }
+}
+
+impl<T: Ord> SpecExtend<BinaryHeap<T>> for BinaryHeap<T> {
+    fn spec_extend(&mut self, ref mut other: BinaryHeap<T>) {
+        self.append(other);
+    }
+}
+
+impl<T: Ord> BinaryHeap<T> {
+    fn extend_desugared<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        let iterator = iter.into_iter();
+        let (lower, _) = iterator.size_hint();
+
+        self.reserve(lower);
+
+        for elem in iterator {
+            self.push(elem);
+        }
+    }
+}
+
+#[stable(feature = "extend_ref", since = "1.2.0")]
+impl<'a, T: 'a + Ord + Copy> Extend<&'a T> for BinaryHeap<T> {
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().cloned());
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+pub struct BinaryHeapPlace<'a, T: 'a>
+where T: Clone + Ord {
+    heap: *mut BinaryHeap<T>,
+    place: vec::PlaceBack<'a, T>,
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T: Clone + Ord + fmt::Debug> fmt::Debug for BinaryHeapPlace<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_tuple("BinaryHeapPlace")
+         .field(&self.place)
+         .finish()
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T: 'a> Placer<T> for &'a mut BinaryHeap<T>
+where T: Clone + Ord {
+    type Place = BinaryHeapPlace<'a, T>;
+
+    fn make_place(self) -> Self::Place {
+        let ptr = self as *mut BinaryHeap<T>;
+        let place = Placer::make_place(self.data.place_back());
+        BinaryHeapPlace {
+            heap: ptr,
+            place: place,
+        }
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T> Place<T> for BinaryHeapPlace<'a, T>
+where T: Clone + Ord {
+    fn pointer(&mut self) -> *mut T {
+        self.place.pointer()
+    }
+}
+
+#[unstable(feature = "collection_placement",
+           reason = "placement protocol is subject to change",
+           issue = "30172")]
+impl<'a, T> InPlace<T> for BinaryHeapPlace<'a, T>
+where T: Clone + Ord {
+    type Owner = &'a T;
+
+    unsafe fn finalize(self) -> &'a T {
+        self.place.finalize();
+
+        let heap: &mut BinaryHeap<T> = &mut *self.heap;
+        let len = heap.len();
+        let i = heap.sift_up(0, len - 1);
+        heap.data.get_unchecked(i)
+    }
+}