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|
/// A priority queue implemented with a binary heap
use core::cmp::Ord;
pub struct PriorityQueue <T: Copy Ord>{
priv data: ~[T],
}
impl <T: Copy Ord> PriorityQueue<T> {
/// Returns the greatest item in the queue - fails if empty
pure fn top(&self) -> T { self.data[0] }
/// Returns the greatest item in the queue - None if empty
pure fn maybe_top(&self) -> Option<T> {
if self.is_empty() { None } else { Some(self.top()) }
}
/// Returns the length of the queue
pure fn len(&self) -> uint { self.data.len() }
/// Returns true if a queue contains no elements
pure fn is_empty(&self) -> bool { self.data.is_empty() }
/// Returns true if a queue contains some elements
pure fn is_not_empty(&self) -> bool { self.data.is_not_empty() }
/// Returns the number of elements the queue can hold without reallocating
pure fn capacity(&self) -> uint { vec::capacity(&self.data) }
fn reserve(&mut self, n: uint) { vec::reserve(&mut self.data, n) }
fn reserve_at_least(&mut self, n: uint) {
vec::reserve_at_least(&mut self.data, n)
}
/// Drop all items from the queue
fn clear(&mut self) { self.data.truncate(0) }
/// Pop the greatest item from the queue - fails if empty
fn pop(&mut self) -> T {
let last = self.data.pop();
if self.is_not_empty() {
let ret = self.data[0];
self.data[0] = last;
self.siftup(0);
ret
} else { last }
}
/// Pop the greatest item from the queue - None if empty
fn maybe_pop(&mut self) -> Option<T> {
if self.is_empty() { None } else { Some(self.pop()) }
}
/// Push an item onto the queue
fn push(&mut self, item: T) {
self.data.push(item);
self.siftdown(0, self.len() - 1);
}
/// Optimized version of a push followed by a pop
fn push_pop(&mut self, item: T) -> T {
let mut item = item;
if self.is_not_empty() && self.data[0] > item {
item <-> self.data[0];
self.siftup(0);
}
item
}
/// Optimized version of a pop followed by a push - fails if empty
fn replace(&mut self, item: T) -> T {
let ret = self.data[0];
self.data[0] = item;
self.siftup(0);
ret
}
/// Consume the PriorityQueue and return the underlying vector
pure fn to_vec(self) -> ~[T] { let PriorityQueue{data: v} = self; v }
/// Consume the PriorityQueue and return a vector in sorted (ascending) order
pure fn to_sorted_vec(self) -> ~[T] {
let mut q = self;
let mut end = q.len() - 1;
while end > 0 {
q.data[end] <-> q.data[0];
end -= 1;
unsafe { q.siftup_range(0, end) } // purity-checking workaround
}
q.to_vec()
}
priv fn siftdown(&mut self, startpos: uint, pos: uint) {
let mut pos = pos;
let newitem = self.data[pos];
while pos > startpos {
let parentpos = (pos - 1) >> 1;
let parent = self.data[parentpos];
if newitem > parent {
self.data[pos] = parent;
pos = parentpos;
loop
}
break
}
self.data[pos] = newitem;
}
priv fn siftup_range(&mut self, pos: uint, endpos: uint) {
let mut pos = pos;
let startpos = pos;
let newitem = self.data[pos];
let mut childpos = 2 * pos + 1;
while childpos < endpos {
let rightpos = childpos + 1;
if rightpos < endpos &&
!(self.data[childpos] > self.data[rightpos]) {
childpos = rightpos;
}
self.data[pos] = self.data[childpos];
pos = childpos;
childpos = 2 * pos + 1;
}
self.data[pos] = newitem;
self.siftdown(startpos, pos);
}
priv fn siftup(&mut self, pos: uint) {
self.siftup_range(pos, self.len());
}
}
pub pure fn from_vec<T: Copy Ord>(xs: ~[T]) -> PriorityQueue<T> {
let mut q = PriorityQueue{data: xs,};
let mut n = q.len() / 2;
while n > 0 {
n -= 1;
unsafe { q.siftup(n) }; // purity-checking workaround
}
q
}
#[cfg(test)]
mod tests {
use sort::merge_sort;
use core::cmp::le;
#[test]
fn test_top_and_pop() {
let data = ~[2, 4, 6, 2, 1, 8, 10, 3, 5, 7, 0, 9, 1];
let mut sorted = merge_sort(data, le);
let mut heap = from_vec(data);
while heap.is_not_empty() {
assert heap.top() == sorted.last();
assert heap.pop() == sorted.pop();
}
}
#[test]
fn test_push() {
let mut heap = from_vec(~[2, 4, 9]);
assert heap.len() == 3;
assert heap.top() == 9;
heap.push(11);
assert heap.len() == 4;
assert heap.top() == 11;
heap.push(5);
assert heap.len() == 5;
assert heap.top() == 11;
heap.push(27);
assert heap.len() == 6;
assert heap.top() == 27;
heap.push(3);
assert heap.len() == 7;
assert heap.top() == 27;
heap.push(103);
assert heap.len() == 8;
assert heap.top() == 103;
}
#[test]
fn test_push_pop() {
let mut heap = from_vec(~[5, 5, 2, 1, 3]);
assert heap.len() == 5;
assert heap.push_pop(6) == 6;
assert heap.len() == 5;
assert heap.push_pop(0) == 5;
assert heap.len() == 5;
assert heap.push_pop(4) == 5;
assert heap.len() == 5;
assert heap.push_pop(1) == 4;
assert heap.len() == 5;
}
#[test]
fn test_replace() {
let mut heap = from_vec(~[5, 5, 2, 1, 3]);
assert heap.len() == 5;
assert heap.replace(6) == 5;
assert heap.len() == 5;
assert heap.replace(0) == 6;
assert heap.len() == 5;
assert heap.replace(4) == 5;
assert heap.len() == 5;
assert heap.replace(1) == 4;
assert heap.len() == 5;
}
#[test]
fn test_to_sorted_vec() {
let data = ~[2, 4, 6, 2, 1, 8, 10, 3, 5, 7, 0, 9, 1];
assert from_vec(data).to_sorted_vec() == merge_sort(data, le);
}
#[test]
#[should_fail]
fn test_empty_pop() { let mut heap = from_vec::<int>(~[]); heap.pop(); }
#[test]
fn test_empty_maybe_pop() {
let mut heap = from_vec::<int>(~[]);
assert heap.maybe_pop().is_none();
}
#[test]
#[should_fail]
fn test_empty_top() { from_vec::<int>(~[]).top(); }
#[test]
fn test_empty_maybe_top() {
assert from_vec::<int>(~[]).maybe_top().is_none();
}
#[test]
#[should_fail]
fn test_empty_replace() {
let mut heap = from_vec::<int>(~[]);
heap.replace(5);
}
#[test]
fn test_to_vec() {
let data = ~[1, 3, 5, 7, 9, 2, 4, 6, 8, 0];
let heap = from_vec(copy data);
assert merge_sort(heap.to_vec(), le) == merge_sort(data, le);
}
}
|
