add priority queue implementation (binary heap)

src/libstd/priority_queue.rs

@@ -0,0 +1,271 @@
+
+/// A priority queue implemented with a binary heap
+use core::cmp::Ord;
+use ptr::addr_of;
+
+#[abi = "rust-intrinsic"]
+extern "C" mod rusti {
+    fn move_val_init<T>(dst: &mut T, -src: T);
+}
+
+pub struct PriorityQueue <T: Ord>{
+    priv data: ~[T],
+}
+
+impl <T: Ord> PriorityQueue<T> {
+    /// Returns the greatest item in the queue - fails if empty
+    pure fn top(&self) -> &self/T { &self.data[0] }
+
+    /// Returns the greatest item in the queue - None if empty
+    pure fn maybe_top(&self) -> Option<&self/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 mut item = self.data.pop();
+        if self.is_not_empty() { item <-> self.data[0]; self.siftdown(0); }
+        item
+    }
+
+    /// 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.siftup(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.siftdown(0);
+        }
+        item
+    }
+
+    /// Optimized version of a pop followed by a push - fails if empty
+    fn replace(&mut self, item: T) -> T {
+        let mut item = item;
+        item <-> self.data[0];
+        self.siftdown(0);
+        item
+    }
+
+    /// 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();
+        while end > 1 {
+            end -= 1;
+            q.data[end] <-> q.data[0];
+            unsafe { q.siftdown_range(0, end) } // purity-checking workaround
+        }
+        q.to_vec()
+    }
+
+    /// Create a PriorityQueue from a vector (heapify)
+    static pub pure fn from_vec(xs: ~[T]) -> PriorityQueue<T> {
+        let mut q = PriorityQueue{data: xs,};
+        let mut n = q.len() / 2;
+        while n > 0 {
+            n -= 1;
+            unsafe { q.siftdown(n) }; // purity-checking workaround
+        }
+        q
+    }
+
+    // The implementations of siftup and siftdown use unsafe blocks in order to
+    // move an element out of the vector (leaving behind a junk element), shift
+    // along the others and move it back into the vector over the junk element.
+    // This reduces the constant factor compared to using swaps, which involves
+    // twice as many moves.
+
+    priv fn siftup(&mut self, start: uint, pos: uint) unsafe {
+        let mut pos = pos;
+        let new = move *addr_of(&self.data[pos]);
+
+        while pos > start {
+            let parent = (pos - 1) >> 1;
+            if new > self.data[parent] {
+                rusti::move_val_init(&mut self.data[pos],
+                                     move *addr_of(&self.data[parent]));
+                pos = parent;
+                loop
+            }
+            break
+        }
+        rusti::move_val_init(&mut self.data[pos], move new);
+    }
+
+    priv fn siftdown_range(&mut self, pos: uint, end: uint) unsafe {
+        let mut pos = pos;
+        let start = pos;
+        let new = move *addr_of(&self.data[pos]);
+
+        let mut child = 2 * pos + 1;
+        while child < end {
+            let right = child + 1;
+            if right < end && !(self.data[child] > self.data[right]) {
+                child = right;
+            }
+            rusti::move_val_init(&mut self.data[pos],
+                                 move *addr_of(&self.data[child]));
+            pos = child;
+            child = 2 * pos + 1;
+        }
+        rusti::move_val_init(&mut self.data[pos], move new);
+        self.siftup(start, pos);
+    }
+
+    priv fn siftdown(&mut self, pos: uint) {
+        self.siftdown_range(pos, self.len());
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use sort::merge_sort;
+    use core::cmp::le;
+    use priority_queue::PriorityQueue::from_vec;
+
+    #[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;
+    }
+
+    fn check_to_vec(data: ~[int]) {
+        let heap = from_vec(data);
+        assert merge_sort(heap.to_vec(), le) == merge_sort(data, le);
+        assert heap.to_sorted_vec() == merge_sort(data, le);
+    }
+
+    #[test]
+    fn test_to_vec() {
+        check_to_vec(~[]);
+        check_to_vec(~[5]);
+        check_to_vec(~[3, 2]);
+        check_to_vec(~[2, 3]);
+        check_to_vec(~[5, 1, 2]);
+        check_to_vec(~[1, 100, 2, 3]);
+        check_to_vec(~[1, 3, 5, 7, 9, 2, 4, 6, 8, 0]);
+        check_to_vec(~[2, 4, 6, 2, 1, 8, 10, 3, 5, 7, 0, 9, 1]);
+        check_to_vec(~[9, 11, 9, 9, 9, 9, 11, 2, 3, 4, 11, 9, 0, 0, 0, 0]);
+        check_to_vec(~[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
+        check_to_vec(~[10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]);
+        check_to_vec(~[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 0, 0, 1, 2]);
+        check_to_vec(~[5, 4, 3, 2, 1, 5, 4, 3, 2, 1, 5, 4, 3, 2, 1]);
+    }
+
+    #[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() { let empty = from_vec::<int>(~[]); empty.top(); }
+
+    #[test]
+    fn test_empty_maybe_top() {
+        let empty = from_vec::<int>(~[]);
+        assert empty.maybe_top().is_none();
+    }
+
+    #[test]
+    #[should_fail]
+    fn test_empty_replace() {
+        let mut heap = from_vec::<int>(~[]);
+        heap.replace(5);
+    }
+}

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;