fix: preserve heap order for infinite key priorities

Author: tianrking

Data-Structures/Heap/KeyPriorityQueue.js

@@ -126,7 +126,7 @@ class KeyPriorityQueue {
     let child2Priority = this._getPriorityOrInfinite(child2Pos)
     let currPriority = this._getPriorityOrInfinite(currPos)
 
-    if (currPriority === Infinity) {
+    if (currPos >= this._heap.length) {
       return
     }
 

Data-Structures/Heap/test/KeyPriorityQueueInfinity.test.js

@@ -0,0 +1,134 @@
+import { KeyPriorityQueue } from '../KeyPriorityQueue.js'
+
+describe('KeyPriorityQueue with infinite priorities', () => {
+  const assertHeap = (queue, priorities) => {
+    expect(queue._heap.length).toBe(priorities.size)
+    expect(queue.priorities).toEqual(priorities)
+    expect(new Set(queue._heap)).toEqual(new Set(priorities.keys()))
+    expect(queue.isEmpty()).toBe(priorities.size === 0)
+    for (const key of priorities.keys()) {
+      expect(queue.contains(key)).toBe(true)
+    }
+    for (let child = 1; child < queue._heap.length; child++) {
+      const parent = Math.floor((child - 1) / 2)
+      const parentPriority = priorities.get(queue._heap[parent])
+      const childPriority = priorities.get(queue._heap[child])
+      expect(parentPriority).toBeLessThanOrEqual(childPriority)
+    }
+    if (priorities.size > 0) {
+      const minimum = Math.min(...priorities.values())
+      expect(priorities.get(queue._heap[0])).toBe(minimum)
+    }
+  }
+
+  const popMinimum = (queue, priorities) => {
+    const minimum = Math.min(...priorities.values())
+    const key = queue.pop()
+    expect(priorities.has(key)).toBe(true)
+    expect(priorities.get(key)).toBe(minimum)
+    priorities.delete(key)
+    expect(queue.contains(key)).toBe(false)
+    assertHeap(queue, priorities)
+    return key
+  }
+
+  it.each([
+    [0, 1, Infinity],
+    [0, 2, 1, Infinity],
+    [0, 1, 2, 3, 4, 5, Infinity]
+  ])('sinks an infinite replacement after popping %j', (...values) => {
+    const queue = new KeyPriorityQueue()
+    const priorities = new Map()
+    values.forEach((priority, key) => {
+      queue.push(key, priority)
+      priorities.set(key, priority)
+    })
+    expect(popMinimum(queue, priorities)).toBe(0)
+    while (priorities.size > 0) {
+      popMinimum(queue, priorities)
+    }
+  })
+
+  it('sinks the root when its priority increases to Infinity', () => {
+    const queue = new KeyPriorityQueue()
+    queue.push('root', 0)
+    queue.push('left', 1)
+    queue.push('right', 2)
+    queue.update('root', Infinity)
+    const priorities = new Map([
+      ['root', Infinity],
+      ['left', 1],
+      ['right', 2]
+    ])
+    assertHeap(queue, priorities)
+    expect(popMinimum(queue, priorities)).toBe('left')
+    expect(popMinimum(queue, priorities)).toBe('right')
+    expect(popMinimum(queue, priorities)).toBe('root')
+  })
+
+  it('sinks an internal node past finite descendants', () => {
+    const queue = new KeyPriorityQueue()
+    const priorities = new Map()
+    for (let key = 0; key < 7; key++) {
+      queue.push(key, key)
+      priorities.set(key, key)
+    }
+    queue.update(1, Infinity)
+    priorities.set(1, Infinity)
+    assertHeap(queue, priorities)
+    queue.update(1, -1)
+    priorities.set(1, -1)
+    assertHeap(queue, priorities)
+    expect(popMinimum(queue, priorities)).toBe(1)
+    while (priorities.size > 0) {
+      popMinimum(queue, priorities)
+    }
+  })
+
+  it('drains equal infinite priorities and can be reused', () => {
+    const queue = new KeyPriorityQueue()
+    const priorities = new Map()
+    for (const key of ['a', 'b', 'c', 'd']) {
+      queue.push(key, Infinity)
+      priorities.set(key, Infinity)
+    }
+    assertHeap(queue, priorities)
+    while (priorities.size > 0) {
+      popMinimum(queue, priorities)
+    }
+    queue.update('new', Infinity)
+    priorities.set('new', Infinity)
+    queue.push('finite', -3)
+    priorities.set('finite', -3)
+    assertHeap(queue, priorities)
+    expect(popMinimum(queue, priorities)).toBe('finite')
+    expect(popMinimum(queue, priorities)).toBe('new')
+  })
+
+  it('matches a reference map through mixed updates and extractions', () => {
+    const queue = new KeyPriorityQueue()
+    const priorities = new Map()
+    for (let key = 0; key < 24; key++) {
+      const priority = key % 3 === 0 ? Infinity : key - 12
+      queue.push(key, priority)
+      priorities.set(key, priority)
+    }
+    assertHeap(queue, priorities)
+    for (let step = 0; step < 12; step++) {
+      const key = queue._heap[0]
+      queue.update(key, Infinity)
+      priorities.set(key, Infinity)
+      assertHeap(queue, priorities)
+      const leaf = queue._heap[queue._heap.length - 1]
+      const priority = step % 2 === 0 ? -Infinity : -step
+      queue.update(leaf, priority)
+      priorities.set(leaf, priority)
+      assertHeap(queue, priorities)
+      popMinimum(queue, priorities)
+    }
+    while (priorities.size > 0) {
+      popMinimum(queue, priorities)
+    }
+    expect(queue.priorities.size).toBe(0)
+  })
+})