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Simplify push_pop_{max, min} and replace_{max, min} implementations #8

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merged 3 commits into from
Dec 19, 2021
Merged

Simplify push_pop_{max, min} and replace_{max, min} implementations #8

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c808bde
Simplify push_pop_* and replace_* implementations
calebsander Sep 4, 2020
5f86071
Add tests for replace_{min,max} edge cases
calebsander Jan 12, 2021
0ba722c
Merge branch 'master' into refactor/replace
tov Dec 19, 2021
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151 changes: 102 additions & 49 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -118,7 +118,7 @@ impl<T: Ord> MinMaxHeap<T> {
} else {
Some(PeekMinMut {
heap: self,
removed: false,
sift: false,
})
}
}
Expand All @@ -141,7 +141,7 @@ impl<T: Ord> MinMaxHeap<T> {
self.find_max().map(move |i| PeekMaxMut {
heap: self,
max_index: i,
removed: false,
sift: false,
})
}

Expand Down Expand Up @@ -212,12 +212,11 @@ impl<T: Ord> MinMaxHeap<T> {
///
/// *O*(log *n*).
pub fn push_pop_min(&mut self, mut element: T) -> T {
if self.is_empty() { return element; }

if element < self.0[0] { return element; }

mem::swap(&mut element, &mut self.0[0]);
self.trickle_down_min(0);
if let Some(mut min) = self.peek_min_mut() {
if element > *min {
mem::swap(&mut element, &mut min);
}
}
element
}

Expand Down Expand Up @@ -245,18 +244,11 @@ impl<T: Ord> MinMaxHeap<T> {
///
/// *O*(log *n*).
pub fn push_pop_max(&mut self, mut element: T) -> T {
if let Some(i) = self.find_max() {
if element > self.0[i] { return element }

mem::swap(&mut element, &mut self.0[i]);

if self.0[i] < self.0[0] {
self.0.swap(0, i);
if let Some(mut max) = self.peek_max_mut() {
if element < *max {
mem::swap(&mut element, &mut max);
}

self.trickle_down_max(i);
}

element
}

Expand Down Expand Up @@ -284,12 +276,15 @@ impl<T: Ord> MinMaxHeap<T> {
/// <struct.MinMaxHeap.html#method.push_pop_min>
///
/// *O*(log *n*).
pub fn replace_min(&mut self, mut element: T) -> Option<T> { if
self.is_empty() { self.push(element); return None; }
pub fn replace_min(&mut self, mut element: T) -> Option<T> {
if let Some(mut min) = self.peek_min_mut() {
mem::swap(&mut element, &mut min);
return Some(element);
}

mem::swap(&mut element, &mut self.0[0]);
self.trickle_down_min(0);
Some(element)
// Heap was empty, so no reordering is neessary
self.0.push(element);
None
}

/// Pops the maximum element and pushes a new element, in an
Expand Down Expand Up @@ -317,19 +312,22 @@ impl<T: Ord> MinMaxHeap<T> {
///
/// *O*(log *n*).
pub fn replace_max(&mut self, mut element: T) -> Option<T> {
if let Some(i) = self.find_max() {
mem::swap(&mut element, &mut self.0[i]);

if self.0[i] < self.0[0] {
self.0.swap(0, i);
if let Some(mut max) = self.peek_max_mut() {
// If `element` is the new min, swap it with the current min
// (unless the min is the same as the max)
if max.heap.len() > 1 {
let min = &mut max.heap.0[0];
if element < *min {
mem::swap(&mut element, min);
}
}

self.trickle_down_max(i);
Some(element)
} else {
self.push(element);
None
mem::swap(&mut element, &mut max);
return Some(element);
}

// Heap was empty, so no reordering is neessary
self.0.push(element);
None
}

/// Returns an ascending (sorted) vector, reusing the heap’s
Expand Down Expand Up @@ -480,7 +478,7 @@ impl<T> MinMaxHeap<T> {
/// Returns a draining iterator over the min-max-heap’s elements in
/// descending (max-first) order.
///
/// *O*(1) on creation, and *O*(log *n*) for each `next()` operation.
/// *<<1) on creation, and *O*(log *n*) for each `next()` operation.
pub fn drain_desc(&mut self) -> DrainDesc<T> {
DrainDesc(self)
}
Expand Down Expand Up @@ -690,7 +688,7 @@ impl<'a, T: Ord + Clone + 'a> Extend<&'a T> for MinMaxHeap<T> {
/// [`MinMaxHeap`]: struct.MinMaxHeap.html
pub struct PeekMinMut<'a, T: 'a + Ord> {
heap: &'a mut MinMaxHeap<T>,
removed: bool,
sift: bool,
}

impl<T: Ord + fmt::Debug> fmt::Debug for PeekMinMut<'_, T> {
Expand All @@ -703,7 +701,7 @@ impl<T: Ord + fmt::Debug> fmt::Debug for PeekMinMut<'_, T> {

impl<'a, T: Ord> Drop for PeekMinMut<'a, T> {
fn drop(&mut self) {
if !self.removed {
if self.sift {
self.heap.trickle_down_min(0);
}
}
Expand All @@ -721,6 +719,7 @@ impl<'a, T: Ord> Deref for PeekMinMut<'a, T> {
impl<'a, T: Ord> DerefMut for PeekMinMut<'a, T> {
fn deref_mut(&mut self) -> &mut T {
debug_assert!(!self.heap.is_empty());
self.sift = true;
// SAFE: PeekMinMut is only instantiated for non-empty heaps
unsafe { self.heap.0.get_unchecked_mut(0) }
}
Expand All @@ -729,9 +728,9 @@ impl<'a, T: Ord> DerefMut for PeekMinMut<'a, T> {
impl<'a, T: Ord> PeekMinMut<'a, T> {
/// Removes the peeked value from the heap and returns it.
pub fn pop(mut self) -> T {
let value = self.heap.pop_min().unwrap();
self.removed = true;
value
// Sift is unnecessary since pop_min() already reorders heap
self.sift = false;
self.heap.pop_min().unwrap()
}
}

Expand All @@ -746,7 +745,7 @@ impl<'a, T: Ord> PeekMinMut<'a, T> {
pub struct PeekMaxMut<'a, T: 'a + Ord> {
heap: &'a mut MinMaxHeap<T>,
max_index: usize,
removed: bool,
sift: bool,
}

impl<T: Ord + fmt::Debug> fmt::Debug for PeekMaxMut<'_, T> {
Expand All @@ -759,14 +758,18 @@ impl<T: Ord + fmt::Debug> fmt::Debug for PeekMaxMut<'_, T> {

impl<'a, T: Ord> Drop for PeekMaxMut<'a, T> {
fn drop(&mut self) {
if !self.removed {
if self.sift {
let mut hole = Hole::new(&mut self.heap.0, self.max_index);

if hole.element() < hole.get_parent() {
hole.swap_with_parent();
}
// If the hole doesn't have a parent, the heap has a single element,
// so no reordering is necessary
if hole.has_parent() {
if hole.element() < hole.get_parent() {
hole.swap_with_parent();
}

hole.trickle_down_max();
hole.trickle_down_max();
}
}
}
}
Expand All @@ -783,6 +786,7 @@ impl<'a, T: Ord> Deref for PeekMaxMut<'a, T> {
impl<'a, T: Ord> DerefMut for PeekMaxMut<'a, T> {
fn deref_mut(&mut self) -> &mut T {
debug_assert!(self.max_index < self.heap.len());
self.sift = true;
// SAFE: PeekMaxMut is only instantiated for non-empty heaps
unsafe { self.heap.0.get_unchecked_mut(self.max_index) }
}
Expand All @@ -791,9 +795,9 @@ impl<'a, T: Ord> DerefMut for PeekMaxMut<'a, T> {
impl<'a, T: Ord> PeekMaxMut<'a, T> {
/// Removes the peeked value from the heap and returns it.
pub fn pop(mut self) -> T {
let value = self.heap.pop_max().unwrap();
self.removed = true;
value
// Sift is unnecessary since pop_max() already reorders heap
self.sift = false;
self.heap.pop_max().unwrap()
}
}

Expand Down Expand Up @@ -900,6 +904,31 @@ mod tests {
result
}

#[test]
fn replace_min() {
let mut h = MinMaxHeap::from(vec![1, 2]);
assert_eq!(Some(1), h.replace_min(0));
assert_eq!(Some(&0), h.peek_min());
assert_eq!(Some(&2), h.peek_max());

assert_eq!(Some(0), h.replace_min(3));
assert_eq!(Some(&2), h.peek_min());
assert_eq!(Some(&3), h.peek_max());
}

#[test]
fn replace_min_edge_cases() {
let mut empty_heap = MinMaxHeap::new();
assert_eq!(None, empty_heap.replace_min(1));
assert_eq!(Some(1), empty_heap.pop_min());
assert_eq!(None, empty_heap.pop_min());

let mut one_element_heap = MinMaxHeap::from(vec![2]);
assert_eq!(Some(2), one_element_heap.replace_min(1));
assert_eq!(Some(1), one_element_heap.pop_min());
assert_eq!(None, one_element_heap.pop_min());
}

#[test]
fn replace_max() {
let mut h = MinMaxHeap::from(vec![1, 2]);
Expand All @@ -912,6 +941,19 @@ mod tests {
assert_eq!(Some(&1), h.peek_max());
}

#[test]
fn replace_max_edge_cases() {
let mut empty_heap = MinMaxHeap::new();
assert_eq!(None, empty_heap.replace_max(1));
assert_eq!(Some(1), empty_heap.pop_max());
assert_eq!(None, empty_heap.pop_max());

let mut one_element_heap = MinMaxHeap::from(vec![1]);
assert_eq!(Some(1), one_element_heap.replace_max(2));
assert_eq!(Some(2), one_element_heap.pop_max());
assert_eq!(None, one_element_heap.pop_max());
}

#[test]
fn peek_min_mut() {
let mut h = MinMaxHeap::from(vec![2, 3, 4]);
Expand Down Expand Up @@ -944,6 +986,17 @@ mod tests {
assert_eq!(Some(&0), h.peek_max());
}

#[test]
fn peek_max_mut_one() {
let mut h = MinMaxHeap::from(vec![1]);
{
let mut max = h.peek_max_mut().unwrap();
assert_eq!(*max, 1);
*max = 2;
}
assert_eq!(h.peek_max(), Some(&2));
}

#[test]
fn push_pop_max() {
let mut h = MinMaxHeap::from(vec![1, 2]);
Expand Down