347.前-k-个高频元素 (二刷)

Author: w2xi

vs-lt/347.前-k-个高频元素.js

@@ -0,0 +1,115 @@
+/*
+ * @lc app=leetcode.cn id=347 lang=javascript
+ *
+ * [347] 前 K 个高频元素
+ */
+
+// @lc code=start
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function(nums, k) {
+  const map = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const curr = nums[i];
+    map.set(curr, (map.get(curr) || 0) + 1);
+  }
+
+  // 优先队列 (小顶堆)
+  const heap = new MinHeap();
+
+  for (const item of map.entries()) {
+    heap.push(item);
+
+    if (heap.size() > k) {
+      heap.pop();
+    }
+  }
+
+  const result = [];
+
+  for (let i = heap.size() - 1; i >= 0; i--) {
+    const item = heap.pop();
+    result.push(item[0]);
+  }
+
+  return result;
+};
+
+class MinHeap {
+  constructor() {
+    this.queue = [];
+  }
+
+  push(item) {
+    if (item) {
+      this.queue.push(item);
+      // 执行上移操作
+      this.siftUp(this.size() - 1);
+    }
+  }
+
+  pop() {
+    if (this.size() === 0) {
+      return undefined;
+    }
+    if (this.size() === 1) {
+      return this.queue.pop();
+    }
+    // 被移除值(堆顶)
+    const removedValue = this.queue[0];
+    // 弹出队列尾部的元素, 放到队头
+    this.queue[0] = this.queue.pop();
+    // 执行下沉操作
+    this.siftDown(0);
+
+    return removedValue;
+  }
+
+  // 上移操作
+  siftUp(index) {
+    const parentIndex = index === 0 ? null : (index - 1) >> 1;
+    const parentValue = this.queue[parentIndex];
+    const currValue = this.queue[index];
+
+    if (index > 0 && currValue[1] < parentValue[1]) {
+      swap(this.queue, index, parentIndex);
+      // 继续执行上移操作
+      this.siftUp(parentIndex);
+    }
+  }
+
+  // 下移
+  siftDown(index) {
+    const left = index * 2 + 1;
+    const right = index * 2 + 2;
+    const size = this.size();
+    let largest = index;
+
+    if (left < size && this.queue[left][1] < this.queue[largest][1]) {
+      largest = left;
+    }
+    if (right < size && this.queue[right][1] < this.queue[largest][1]) {
+      largest = right;
+    }
+
+    if (largest !== index) {
+      swap(this.queue, index, largest);
+      this.siftDown(largest);
+    }
+  }
+
+  size() {
+    return this.queue.length;
+  }
+}
+
+function swap(array, i, j) {
+  const temp = array[i];
+  array[i] = array[j];
+  array[j] = temp;
+}
+// @lc code=end