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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| //! A priority queue where the priorities are indices (small non-negative integers). | ||
| use std::collections::VecDeque; | ||
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|
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| /// A priority queue where the priorities are indices (small non-negative integers). | ||
| /// | ||
| /// Larger indices are higher priority. | ||
| pub struct IndexedQueue<T> { | ||
| /// Invariant: the last `VecDeque` is non-empty. | ||
| queues: Vec<VecDeque<T>>, | ||
| } | ||
| impl<T> Default for IndexedQueue<T> { | ||
| fn default() -> Self { | ||
| Self { queues: Vec::new() } | ||
| } | ||
| } | ||
| impl<T> IndexedQueue<T> { | ||
| /// Creates a new `IndexedQueue`. | ||
| pub fn new() -> Self { | ||
| Self::default() | ||
| } | ||
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| /// Pushes an element to the queue with the given index. | ||
| pub fn push(&mut self, index: usize, element: T) { | ||
| if index >= self.queues.len() { | ||
| self.queues.resize_with(index + 1, Default::default); | ||
| } | ||
| self.queues[index].push_back(element); | ||
| } | ||
|
|
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| /// Pops an element from the queue with the largest index. | ||
| pub fn pop(&mut self) -> Option<(usize, T)> { | ||
| let item = self.queues.last_mut()?.pop_front().unwrap(); | ||
| let index = self.queues.len() - 1; | ||
| // Remove trailing empty queues to maintain the invariant. | ||
| while self.queues.last().is_some_and(VecDeque::is_empty) { | ||
| self.queues.pop(); | ||
| } | ||
| Some((index, item)) | ||
| } | ||
|
|
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| /// Returns the number of elements in the `IndexedQueue`. | ||
| pub fn len(&self) -> usize { | ||
| self.queues.iter().map(VecDeque::len).sum() | ||
| } | ||
|
|
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| /// Returns `true` if the `IndexedQueue` is empty. | ||
| pub fn is_empty(&self) -> bool { | ||
| self.queues.is_empty() | ||
| } | ||
| } | ||
|
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| #[cfg(test)] | ||
| mod test { | ||
| use super::*; | ||
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| #[test] | ||
| fn test_indexed_queue() { | ||
| let mut queue = IndexedQueue::new(); | ||
| assert_eq!(queue.len(), 0); | ||
| assert!(queue.is_empty()); | ||
|
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| queue.push(0, 0); | ||
| queue.push(1, 1); | ||
| queue.push(0, 2); | ||
| queue.push(5, 3); | ||
| queue.push(1, 4); | ||
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| assert_eq!(queue.len(), 5); | ||
| assert!(!queue.is_empty()); | ||
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| assert_eq!(queue.pop(), Some((5, 3))); | ||
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| assert_eq!(queue.len(), 4); | ||
| assert!(!queue.is_empty()); | ||
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| assert_eq!(queue.pop(), Some((1, 1))); | ||
| assert_eq!(queue.pop(), Some((1, 4))); | ||
| assert_eq!(queue.pop(), Some((0, 0))); | ||
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| assert_eq!(queue.len(), 1); | ||
| assert!(!queue.is_empty()); | ||
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| assert_eq!(queue.pop(), Some((0, 2))); | ||
| assert_eq!(queue.pop(), None); | ||
|
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| assert_eq!(queue.len(), 0); | ||
| assert!(queue.is_empty()); | ||
| } | ||
| } |
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