| 1 | /** |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * |
| 4 | * This source code is licensed under the MIT license found in the |
| 5 | * LICENSE file in the root directory of this source tree. |
| 6 | * |
| 7 | * @flow strict |
| 8 | */ |
| 9 | |
| 10 | type Heap<T: Node> = Array<T>; |
| 11 | type Node = { |
| 12 | id: number, |
| 13 | sortIndex: number, |
| 14 | ... |
| 15 | }; |
| 16 | |
| 17 | export function push<T: Node>(heap: Heap<T>, node: T): void { |
| 18 | const index = heap.length; |
| 19 | heap.push(node); |
| 20 | siftUp(heap, node, index); |
| 21 | } |
| 22 | |
| 23 | export function peek<T: Node>(heap: Heap<T>): T | null { |
| 24 | return heap.length === 0 ? null : heap[0]; |
| 25 | } |
| 26 | |
| 27 | export function pop<T: Node>(heap: Heap<T>): T | null { |
| 28 | if (heap.length === 0) { |
| 29 | return null; |
| 30 | } |
| 31 | const first = heap[0]; |
| 32 | const last = heap.pop(); |
| 33 | if (last !== first) { |
| 34 | // $FlowFixMe[incompatible-type] |
| 35 | heap[0] = last; |
| 36 | // $FlowFixMe[incompatible-type] |
| 37 | siftDown(heap, last, 0); |
| 38 | } |
| 39 | return first; |
| 40 | } |
| 41 | |
| 42 | function siftUp<T: Node>(heap: Heap<T>, node: T, i: number): void { |
| 43 | let index = i; |
| 44 | while (index > 0) { |
| 45 | const parentIndex = (index - 1) >>> 1; |
| 46 | const parent = heap[parentIndex]; |
| 47 | if (compare(parent, node) > 0) { |
| 48 | // The parent is larger. Swap positions. |
| 49 | heap[parentIndex] = node; |
| 50 | heap[index] = parent; |
| 51 | index = parentIndex; |
| 52 | } else { |
| 53 | // The parent is smaller. Exit. |
| 54 | return; |
| 55 | } |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | function siftDown<T: Node>(heap: Heap<T>, node: T, i: number): void { |
| 60 | let index = i; |
| 61 | const length = heap.length; |
| 62 | const halfLength = length >>> 1; |
| 63 | while (index < halfLength) { |
| 64 | const leftIndex = (index + 1) * 2 - 1; |
| 65 | const left = heap[leftIndex]; |
| 66 | const rightIndex = leftIndex + 1; |
| 67 | const right = heap[rightIndex]; |
| 68 | |
| 69 | // If the left or right node is smaller, swap with the smaller of those. |
| 70 | if (compare(left, node) < 0) { |
| 71 | if (rightIndex < length && compare(right, left) < 0) { |
| 72 | heap[index] = right; |
| 73 | heap[rightIndex] = node; |
| 74 | index = rightIndex; |
| 75 | } else { |
| 76 | heap[index] = left; |
| 77 | heap[leftIndex] = node; |
| 78 | index = leftIndex; |
| 79 | } |
| 80 | } else if (rightIndex < length && compare(right, node) < 0) { |
| 81 | heap[index] = right; |
| 82 | heap[rightIndex] = node; |
| 83 | index = rightIndex; |
| 84 | } else { |
| 85 | // Neither child is smaller. Exit. |
| 86 | return; |
| 87 | } |
| 88 | } |
| 89 | } |
| 90 | |
| 91 | function compare(a: Node, b: Node) { |
| 92 | // Compare sort index first, then task id. |
| 93 | const diff = a.sortIndex - b.sortIndex; |
| 94 | return diff !== 0 ? diff : a.id - b.id; |
| 95 | } |