<commit_before>
/// 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) -> &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()
    }

    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
    }

    priv fn siftup(&mut self, start: uint, pos: uint) {
        let mut pos = pos;
        let new = self.data[pos];

        while pos > start {
            let parent = (pos - 1) >> 1;
            if new > self.data[parent] {
                self.data[pos] = self.data[parent];
                pos = parent;
                loop
            }
            break
        }
        self.data[pos] = new;
    }

    priv fn siftdown_range(&mut self, pos: uint, end: uint) {
        let mut pos = pos;
        let start = pos;
        let new = 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;
            }
            self.data[pos] = self.data[child];
            pos = child;
            child = 2 * pos + 1;
        }
        self.data[pos] = new;
        self.siftup(start, pos);
    }

    priv fn siftdown(&mut self, pos: uint) {
        self.siftdown_range(pos, self.len());<commit_msg>priority_queue: replace copies with moves<commit_after>
/// 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()
    }

    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());
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