[0347.前K个高频元素] 添加js版本代码

problems/0347.前K个高频元素.md

@@ -190,6 +190,101 @@ class Solution:
 Go：
 
 
+javaScript:
+```js
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function(nums, k) {
+  const map = new Map();
+  
+  for(const num of nums) {
+    map.set(num, (map.get(num) || 0) + 1);
+  }
+
+  // 创建小顶堆
+  const priorityQueue = new PriorityQueue((a, b) => a[1] - b[1]);
+
+  // entry 是一个长度为2的数组，0位置存储key，1位置存储value
+  for (const entry of map.entries()) {
+    priorityQueue.push(entry);
+    if (priorityQueue.size() > k) {
+      priorityQueue.pop();
+    }
+  }
+
+  const ret = [];
+
+  for(let i = priorityQueue.size() - 1; i >= 0; i--) {
+    ret[i] = priorityQueue.pop()[0];
+  }
+
+  return ret;
+};
+
+
+function PriorityQueue(compareFn) {
+  this.compareFn = compareFn;
+  this.queue = [];
+}
+
+// 添加
+PriorityQueue.prototype.push = function(item) {
+  this.queue.push(item);
+  let index = this.queue.length - 1;
+  let parent = Math.floor((index - 1) / 2);
+  // 上浮
+  while(parent >= 0 && this.compare(parent, index) > 0) {
+    // 交换
+    [this.queue[index], this.queue[parent]] = [this.queue[parent], this.queue[index]];
+    index = parent;
+    parent = Math.floor((index - 1) / 2);
+  }
+}
+
+// 获取堆顶元素并移除
+PriorityQueue.prototype.pop = function() {
+  const ret = this.queue[0];
+
+  // 把最后一个节点移到堆顶
+  this.queue[0] = this.queue.pop();
+
+  let index = 0;
+  // 左子节点下标，left + 1 就是右子节点下标
+  let left = 1;
+  let selectedChild = this.compare(left, left + 1) > 0 ? left + 1 : left;
+
+  // 下沉
+  while(selectedChild !== undefined && this.compare(index, selectedChild) > 0) {
+    // 交换
+    [this.queue[index], this.queue[selectedChild]] = [this.queue[selectedChild], this.queue[index]];
+    index = selectedChild;
+    left = 2 * index + 1;
+    selectedChild = this.compare(left, left + 1) > 0 ? left + 1 : left;
+  }
+
+  return ret;
+}
+
+PriorityQueue.prototype.size = function() {
+  return this.queue.length;
+}
+
+// 使用传入的 compareFn 比较两个位置的元素
+PriorityQueue.prototype.compare = function(index1, index2) {
+  if (this.queue[index1] === undefined) {
+    return 1;
+  }
+  if (this.queue[index2] === undefined) {
+    return -1;
+  }
+
+  return this.compareFn(this.queue[index1], this.queue[index2]);
+}
+```
+
 
 
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