LeetCode：215. 数组中的第K个最大元素

使用最小堆方法

/**
 * JavaScript 实现：最小堆类
 * 插入
 * 删除
 * 返回堆头
 * 返回堆长
 */

class MinHeap {
    constructor() {
        this.heap = []
    }

    swap(i1, i2) {
        // 交换两个值
        const temp = this.heap[i1]
        this.heap[i1] = this.heap[i2]
        this.heap[i2] = temp
    }

    getParentIndex(i) {
        // 获取父元素的索引值 (index-1)/2
        // 类似 Math.floor((index-1/2))
        return (i - 1) >> 1
    }

    getLeftIndex(i) {
        // 获取左元素的索引值 i*2+1
        // 类似 Math.floor((index-1/2))
        return i * 2 + 1
    }

    getRightIndex(i) {
        // 获取右元素的索引值 i*2+2
        // 类似 Math.floor((index-1/2))
        return i * 2 + 2
    }

    shiftUp(index) {
        if (index === 0) return;

        const parentIndex = this.getParentIndex(index)

        // 较小的值 上移
        if (this.heap[index] < this.heap[parentIndex]) {
            this.swap(index, parentIndex)
            this.shiftUp(parentIndex)
        }
    }

    shiftDown(index) {
        const leftIndex = this.getLeftIndex(index)
        const rightIndex = this.getRightIndex(index)

        // 较大的值 下移
        if (this.heap[index] > this.heap[leftIndex]) {
            this.swap(index, leftIndex)
            this.shiftDown(leftIndex)
        }

        // 较大的值 下移
        if (this.heap[index] > this.heap[rightIndex]) {
            this.swap(index, rightIndex)
            this.shiftDown(rightIndex)
        }
    }

    insert(val) {
        // 插入新值
        this.heap.push(val)
        this.shiftUp(this.heap.length - 1)
    }
    pop() {
        // 删除值，用堆尾替换堆顶
        this.heap[0] = this.heap.pop()

        // 然后把较大值下移
        this.shiftDown(0)
    }
    peek() {
        // 返回堆顶
        return this.heap[0]
    }

    size() {
        // 返回堆容量
        return this.heap.length
    }
}

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
var findKthLargest = function (nums, k) {
    const heap = new MinHeap()

    nums.forEach(n => {
        heap.insert(n)
        if (heap.size() > k) {
            heap.pop()
        }

        console.log(heap)
    })

    return heap.peek()
};