[gyim1345] max-heap 구현

자료구조/heap/MaxHeap.test.js

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+class MaxHeap {
+  constructor() {
+    this.items = [];
+  }
+
+  getLeftChildIndex(parentIndex) {
+    return 2 * parentIndex + 1;
+  }
+
+  getRightChildIndex(parentIndex) {
+    return 2 * parentIndex + 2;
+  }
+
+  getParentIndex(childIndex) {
+    return Math.floor((childIndex - 1) / 2);
+  }
+
+  hasLeftChild(currentIndex) {
+    return this.getLeftChildIndex(currentIndex) <= this.items.length - 1;
+  }
+
+  hasRightChild(currentIndex) {
+    return this.getRightChildIndex(currentIndex) <= this.items.length - 1;
+  }
+
+  hasParent(currentIndex) {
+    return this.getParentIndex(currentIndex) <= this.items.length - 1;
+  }
+
+  getLeftChild(index) {
+    return this.items[this.getLeftChildIndex(index)];
+  }
+
+  getRightChild(index) {
+    return this.items[this.getRightChildIndex(index)];
+  }
+
+  getParent(index) {
+    return this.items[this.getParentIndex(index)];
+  }
+
+  swap(indexOne, indexTwo) {
+    let temp = this.items[indexOne];
+    this.items[indexOne] = this.items[indexTwo];
+    this.items[indexTwo] = temp;
+  }
+
+  isEmpty() {
+    return this.items.length === 0;
+  }
+  peek() {
+    if (this.isEmpty()) {
+      return;
+    }
+    return this.items[0];
+  }
+
+  remove() {
+    if (this.isEmpty()) {
+      return;
+    }
+    if (this.items.length === 1) {
+      return this.items.pop();
+    }
+    const item = this.items.pop();
+    const removed = this.items[0];
+    this.items[0] = item;
+
+    this.heapifyDownward();
+    return removed;
+  }
+
+  insert(item) {
+    this.items.push(item);
+    this.heapifyUpward();
+  }
+
+  heapifyUpward() {
+    let currentIndex = this.items.length - 1;
+    while (this.getParent(currentIndex) < this.items[currentIndex]) {
+      this.swap(this.getParentIndex(currentIndex), currentIndex);
+      currentIndex = this.getParentIndex(currentIndex);
+    }
+  }
+
+  heapifyDownward() {
+    let currentIndex = 0;
+    while (this.hasLeftChild(currentIndex)) {
+      let greaterChildIndex = this.getLeftChildIndex(currentIndex);
+      if (
+        this.hasRightChild(currentIndex) &&
+        this.getRightChild(currentIndex) > this.getLeftChild(currentIndex)
+      ) {
+        greaterChildIndex = this.getRightChildIndex(currentIndex);
+      }
+      if (this.items[currentIndex] > this.items[greaterChildIndex]) {
+        break;
+      }
+      this.swap(currentIndex, greaterChildIndex);
+      currentIndex = greaterChildIndex;
+    }
+  }
+
+  toArray() {
+    return this.items;
+  }
+}
+
+module.exports = MaxHeap;
+
+test('insert', () => {
+  const heap = new MaxHeap();
+  [6, 5, 3, 1, 8, 7, 2, 4].forEach((value) => heap.insert(value));
+  expect(heap.toArray()).toEqual([8, 6, 7, 4, 5, 3, 2, 1]);
+});
+test('remove', () => {
+  const heap = new MaxHeap();
+  [6, 5, 3, 1, 8, 7, 2, 4].forEach((value) => heap.insert(value));
+  [8, 7, 6, 5, 4, 3, 2, 1].forEach((value) => {
+    expect(heap.remove()).toBe(value);
+  });
+});