JS手写最小堆（小顶堆）、最大堆（大顶堆）

最小堆有两个方法：插入和移出。
插入：将元素放置在堆的末尾，递归地将它与父节点元素对比，如果其值比父节点小就交换位置，直至其值大于等于父节点或移至到堆的首部。
移出：堆中最小的值位于堆顶，先将其与堆尾元素交换位置，移出堆尾元素；将堆顶元素递归地与左右子节点元素比较，如果其值大于子节点就交换位置，直至其值小于等于子节点。

let heap = [];

function swap(index1, index2) {

    [heap[index1], heap[index2]] = [heap[index2], heap[index1]]

}

function shiftup(index) {

    let parentIndex = Math.floor((index - 1) / 2);

    if (index != 0 && heap[parentIndex] > heap[index]) {

        swap(parentIndex, index);

        shiftup(parentIndex);

    }

}

function shiftDown(index) {

    let leftNodeIndex = (index + 1) * 2 - 1, rightNodeIndex = (index + 1) * 2

    if (leftNodeIndex < heap.length && heap[leftNodeIndex] < heap[index]) {

        swap(leftNodeIndex, index);

        shiftDown(leftNodeIndex);

    }

    if (rightNodeIndex < heap.length && heap[rightNodeIndex] < heap[index]) {

        swap(rightNodeIndex, index);

        shiftDown(rightNodeIndex);

    }

}

function insert(val) {

    heap.push(val);

    shiftup(heap.length - 1);

}

function remove() {

    swap(0, heap.length - 1);

    let temp = heap.pop();

    shiftDown(0);

    return temp;

}

最大堆与最小堆的实现思路一样，只是需要父子节点交换的条件不同；最大堆的最大值位于堆顶，所以需要在父节点小于子节点时进行交换位置。

let heap = [];

function swap(index1, index2) {

    [heap[index1], heap[index2]] = [heap[index2], heap[index1]]

}

function shiftup(index) {

    let parentIndex = Math.floor((index - 1) / 2);

    if (index != 0 && heap[parentIndex] < heap[index]) {

        swap(parentIndex, index);

        shiftup(parentIndex);

    }

}

function shiftDown(index) {

    let leftNodeIndex = (index + 1) * 2 - 1, rightNodeIndex = (index + 1) * 2

    if (leftNodeIndex < heap.length && heap[leftNodeIndex] > heap[index]) {

        swap(leftNodeIndex, index);

        shiftDown(leftNodeIndex);

    }

    if (rightNodeIndex < heap.length && heap[rightNodeIndex] > heap[index]) {

        swap(rightNodeIndex, index);

        shiftDown(rightNodeIndex);

    }

}

function insert(val) {

    heap.push(val);

    shiftup(heap.length - 1);

}

function remove() {

    swap(0, heap.length - 1);

    let temp = heap.pop();

    shiftDown(0);

    return temp;

}