feat: 数组中第k个最大值(215)

leetcode/中等/数组中第k个最大值.js

@@ -0,0 +1,163 @@
+/*
+215. 数组中的第K个最大元素
+中等
+
+相关标签
+相关企业
+给定整数数组 nums 和整数 k，请返回数组中第 k 个最大的元素。
+
+请注意，你需要找的是数组排序后的第 k 个最大的元素，而不是第 k 个不同的元素。
+
+你必须设计并实现时间复杂度为 O(n) 的算法解决此问题。
+
+示例 1:
+
+输入: [3,2,1,5,6,4], k = 2
+输出: 5
+示例 2:
+
+输入: [3,2,3,1,2,4,5,5,6], k = 4
+输出: 4
+
+提示：
+
+1 <= k <= nums.length <= 105
+-104 <= nums[i] <= 104
+*/
+
+// 思路1:排序之后直接取，但是不符合题目要求
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+const findKthLargest = function (nums, k) {
+  nums.sort((a, b) => a - b);
+  return nums[nums.length - k];
+};
+
+// 使用快速选择算法
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+const partition = (nums, left, right) => {
+  const pivot = nums[right];
+  let i = left;
+  for (let j = left; j < right; j++) {
+    if (nums[j] < pivot) {
+      [nums[i], nums[j]] = [nums[j], nums[i]];
+      i++;
+    }
+  }
+  [nums[i], nums[right]] = [nums[right], nums[i]];
+  return i;
+};
+
+const quickSelect = (nums, left, right, k) => {
+  if (left === right) return nums[left];
+  const pivotIndex = partition(nums, left, right);
+  if (pivotIndex === k) {
+    return nums[k];
+  } if (pivotIndex < k) {
+    return quickSelect(nums, pivotIndex + 1, right, k);
+  }
+  return quickSelect(nums, left, pivotIndex - 1, k);
+};
+
+const findKthLargest2 = function (nums, k) {
+  return quickSelect(nums, 0, nums.length - 1, nums.length - k);
+};
+
+// 使用最小堆
+class MinHeap {
+  constructor() {
+    this.heap = [];
+  }
+
+  size() {
+    return this.heap.length;
+  }
+
+  peek() {
+    return this.heap[0];
+  }
+
+  insert(value) {
+    this.heap.push(value);
+    this.heapifyUp();
+  }
+
+  remove() {
+    if (this.size() === 1) {
+      return this.heap.pop();
+    }
+    const root = this.heap[0];
+    this.heap[0] = this.heap.pop();
+    this.heapifyDown();
+    return root;
+  }
+
+  heapifyUp() {
+    let index = this.size() - 1;
+    while (index > 0) {
+      const parentIndex = Math.floor((index - 1) / 2);
+      if (this.heap[parentIndex] <= this.heap[index]) break;
+      [this.heap[parentIndex], this.heap[index]] = [this.heap[index], this.heap[parentIndex]];
+      index = parentIndex;
+    }
+  }
+
+  heapifyDown() {
+    let index = 0;
+    const length = this.size();
+    const element = this.heap[0];
+    while (true) {
+      const leftChildIndex = 2 * index + 1;
+      const rightChildIndex = 2 * index + 2;
+      let leftChild; let
+        rightChild;
+      let swap = null;
+
+      if (leftChildIndex < length) {
+        leftChild = this.heap[leftChildIndex];
+        if (leftChild < element) {
+          swap = leftChildIndex;
+        }
+      }
+
+      if (rightChildIndex < length) {
+        rightChild = this.heap[rightChildIndex];
+        if ((swap === null && rightChild < element) || (swap !== null && rightChild < leftChild)) {
+          swap = rightChildIndex;
+        }
+      }
+
+      if (swap === null) break;
+      [this.heap[index], this.heap[swap]] = [this.heap[swap], this.heap[index]];
+      index = swap;
+    }
+  }
+}
+
+const findKthLargest3 = function (nums, k) {
+  const minHeap = new MinHeap();
+
+  for (const num of nums) {
+    minHeap.insert(num);
+    if (minHeap.size() > k) {
+      minHeap.remove();
+    }
+  }
+
+  return minHeap.peek();
+};
+
+// 示例测试
+console.log(findKthLargest([3, 2, 1, 5, 6, 4], 2)); // 输出: 5
+console.log(findKthLargest([3, 2, 3, 1, 2, 4, 5, 5, 6], 4)); // 输出: 4
+console.log(findKthLargest2([3, 2, 1, 5, 6, 4], 2)); // 输出: 5
+console.log(findKthLargest2([3, 2, 3, 1, 2, 4, 5, 5, 6], 4)); // 输出: 4
+console.log(findKthLargest3([3, 2, 1, 5, 6, 4], 2)); // 输出: 5
+console.log(findKthLargest3([3, 2, 3, 1, 2, 4, 5, 5, 6], 4)); // 输出: 4