parent= (i-1)/2 (向下取整);
    c1 = 2i + 1;
    c2 = 2    i+2;

    1. // 大根堆排序
    3. let tree = [4,10,3,5,1,2];
    4. let n = 6;
    6. heapify(tree,6,0);
    9. function build_heap(tree, n) {
    10.     let last_node = n - 1;
    12.     let parent = (last_node - 1) / 2;
    14.     for (let i = parent; i >= 0; i--) {
    15.         heapify(tree, n, i);
    16.     }
    17. }
    20. function heapify(tree, n, i) {
    21.     if (i >= n) {
    22.         return;
    23.     }
    24.     let c1 = 2 * i + 1;
    25.     let c2 = 2 * i + 2;
    27.     let max = i;
    29.     if (c1 < n && tree[ci] > tree[max]) {
    30.         max = c1;
    31.     }
    33.     if (c2 < n && tree[c2] > tree[max]) {
    34.         max = c2;
    35.     }
    37.     if (max !== i) {
    38.         swap(tree, max, i);
    39.         heapify(tree, n, max);
    40.     }
    41. }
    43. function swap(tree, i, j) {
    44.     let temp = tree[i];
    46.     tree[i] = tree[j];
    48.     tree[j] = temp;
    49. }
    52. function findKthLargest(nums,k) {
    53.     let len = nums.length;
    54.     build_heap(nums, len);
    55.     let heapsize = len;
    57.     for (let i = len; i >= len - k + 1; i--) {
    58.         swap(nums, 0, i);
    59.         heapsize--;
    60.         heapify(nums, 0, heapsize);
    61.     }
    63.     return nums[0];
    64. }

    讲解视频： https://www.youtube.com/watch?v=j-DqQcNPGbE