From dd2b32be56945824e1e900d9748274633d6db6c1 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Sun, 9 Dec 2012 20:02:33 -0500
Subject: [PATCH] add priority queue implementation (binary heap)

---
 src/libstd/priority_queue.rs | 253 +++++++++++++++++++++++++++++++++++
 src/libstd/std.rc            |   1 +
 2 files changed, 254 insertions(+)
 create mode 100644 src/libstd/priority_queue.rs

diff --git a/src/libstd/priority_queue.rs b/src/libstd/priority_queue.rs
new file mode 100644
index 00000000000..c744ba1ca5c
--- /dev/null
+++ b/src/libstd/priority_queue.rs
@@ -0,0 +1,253 @@
+
+/// 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
+    }
+
+    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());
+    }
+}
+
+/// Consume the PriorityQueue and return the underlying vector
+pub pure fn to_vec<T: Copy Ord>(q: PriorityQueue<T>) -> ~[T] {
+    let PriorityQueue{data: v} = q;
+    v
+}
+
+/// Consume the PriorityQueue and return a vector in sorted (ascending) order
+pub pure fn to_sorted_vec<T: Copy Ord>(q: PriorityQueue<T>) -> ~[T] {
+    let mut q = q;
+    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
+    }
+    to_vec(q)
+}
+
+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 to_sorted_vec(from_vec(data)) == 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(to_vec(heap), le) == merge_sort(data, le);
+    }
+}
diff --git a/src/libstd/std.rc b/src/libstd/std.rc
index 65916aa5992..f5363ca23c5 100644
--- a/src/libstd/std.rc
+++ b/src/libstd/std.rc
@@ -73,6 +73,7 @@ pub mod deque;
 pub mod fun_treemap;
 pub mod list;
 pub mod map;
+pub mod priority_queue;
 pub mod rope;
 pub mod smallintmap;
 pub mod sort;