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//! A priority queue based on a [binomial heap]. //! //! See [`BinomialHeap`](struct.BinomialHeap.html) for details. //! //! [binomial heap]: https://en.wikipedia.org/wiki/Binomial_heap #![deny(missing_docs)] use std::fmt::{self, Debug}; use std::marker::PhantomData; use std::mem; mod node; pub use node::{IntoIter, Iter}; /// A priority queue based on a binomial heap. /// /// Like [`BinaryHeap`], `BionmialHeap` is an implementation of a priority queue. Unlike /// `BinaryHeap`, `BionmialHeap` provides an efficient `append` method, at the cost of greater /// memory usage, slower iteration, and poor cache locality. /// /// # Time Complexity /// /// | Operation | Time Complexity | /// |--------------------------------|------------------------| /// | [`append`](#method.append) | `O(log n)` (amortized) | /// | [`peek`](#method.peek) | `O(log n)` | /// | [`pop`](#method.pop) | `O(log n)` | /// | [`push`](#method.push) | `O(1)` (amortized) | /// | [`push_pop`](#method.push_pop) | `O(log n)` | /// | [`replace`](#method.replace) | `O(log n)` | /// /// [`BinaryHeap`]: https://doc.rust-lang.org/std/collections/struct.BinaryHeap.html pub struct BinomialHeap<T: Ord> { root: Option<Box<node::Node<T>>>, len: usize, } impl<T: Ord> BinomialHeap<T> { /// Returns a new heap. pub fn new() -> Self { BinomialHeap { root: None, len: 0 } } /// Checks if the heap is empty. pub fn is_empty(&self) -> bool { self.root.is_none() } /// Returns the number of items in the heap. pub fn len(&self) -> usize { self.len } /// Returns an iterator that yields references to the items in the heap in arbitrary order. pub fn iter(&self) -> Iter<T> { node::iter(&self.root, self.len) } /// Returns a reference to the greatest item in the heap. /// /// Returns `None` if the heap is empty. pub fn peek(&self) -> Option<&T> { node::peek(&self.root) } /// Pushes the given item onto the heap. pub fn push(&mut self, item: T) { node::push(&mut self.root, item); self.len += 1; } /// Moves the given heap's items into the heap, leaving the given heap empty. /// /// This is equivalent to, but likely to be faster than, the following: /// /// ``` /// # let mut heap = binomial_heap::BinomialHeap::<i32>::new(); /// # let mut heap2 = binomial_heap::BinomialHeap::new(); /// heap.extend(heap2.drain()); /// ``` pub fn append(&mut self, other: &mut Self) { match self.root { None => mem::swap(self, other), Some(ref mut root) => { node::append(root, other.root.take()); self.len += mem::replace(&mut other.len, 0); } } } /// Pushes the given item onto the heap, then removes the greatest item in the heap and returns /// it. /// /// This method is equivalent to, but likely faster than, the following: /// /// ``` /// # let mut heap = binomial_heap::BinomialHeap::new(); /// # let item = 0; /// heap.push(item); /// let max = heap.pop().unwrap(); /// ``` pub fn push_pop(&mut self, item: T) -> T { self.push(item); self.pop().expect("heap was empty") } /// Removes the greatest item in the heap, then pushes the given item onto the heap. /// /// Returns the item that was removed, or `None` if the heap was empty. /// /// This method is equivalent to, but likely faster than, the following: /// /// ``` /// # let mut heap = binomial_heap::BinomialHeap::new(); /// # let item = 0; /// let max = heap.pop(); /// heap.push(item); /// ``` pub fn replace(&mut self, item: T) -> Option<T> { let max = self.pop(); self.push(item); max } /// Removes the greatest item in the heap and returns it. /// /// Returns `None` if the heap was empty. /// /// If a call to this method is immediately preceded by a call to [`push`], consider using /// [`push_pop`] instead. If a call to this method is immediately followed by a call to /// [`push`], consider using [`replace`] instead. /// /// [`push`]: #method.push /// [`push_pop`]: #method.push_pop /// [`replace`]: #method.replace pub fn pop(&mut self) -> Option<T> { node::pop(&mut self.root, &mut self.len) } /// Removes all items from the heap. pub fn clear(&mut self) { *self = Self::new(); } /// Removes all items from the heap and returns an iterator that yields them in arbitrary /// order. /// /// All items are removed even if the iterator is not exhausted. However, the behavior of /// this method is unspecified if the iterator is leaked (e.g. via [`mem::forget`]). /// /// [`mem::forget`]: https://doc.rust-lang.org/std/mem/fn.forget.html pub fn drain(&mut self) -> Drain<T> { Drain { iter: mem::replace(self, Self::new()).into_iter(), marker: PhantomData } } } impl<T: Ord + Debug> Debug for BinomialHeap<T> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_list().entries(self).finish() } } impl<T: Ord> Default for BinomialHeap<T> { fn default() -> Self { Self::new() } } impl<T: Ord> Extend<T> for BinomialHeap<T> { fn extend<I: IntoIterator<Item = T>>(&mut self, items: I) { for item in items { self.push(item); } } } impl<T: Ord> std::iter::FromIterator<T> for BinomialHeap<T> { fn from_iter<I: IntoIterator<Item = T>>(items: I) -> Self { let mut heap = Self::new(); heap.extend(items); heap } } impl<T: Ord> IntoIterator for BinomialHeap<T> { type Item = T; type IntoIter = IntoIter<T>; fn into_iter(self) -> IntoIter<T> { node::into_iter(self.root, self.len) } } impl<'a, T: Ord> IntoIterator for &'a BinomialHeap<T> { type Item = &'a T; type IntoIter = Iter<'a, T>; fn into_iter(self) -> Iter<'a, T> { self.iter() } } /// An iterator that drains a `BinomialHeap`, yielding its items in arbitrary order. /// /// Acquire through [`BinomialHeap::drain`](struct.BinomialHeap.html#method.drain). pub struct Drain<'a, T: 'a> { iter: IntoIter<T>, marker: PhantomData<&'a mut IntoIter<T>>, } impl<'a, T: Ord> Iterator for Drain<'a, T> { type Item = T; fn next(&mut self) -> Option<T> { self.iter.next() } fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() } } impl<'a, T: Ord> ExactSizeIterator for Drain<'a, T> { fn len(&self) -> usize { self.iter.len() } }