LeetCode: Flatten Binary Tree To Linked List Solution

1/**
2 * Definition for a binary tree node.
3 * function TreeNode(val, left, right) {
4 *     this.val = (val===undefined ? 0 : val)
5 *     this.left = (left===undefined ? null : left)
6 *     this.right = (right===undefined ? null : right)
7 * }
8 */
9/**
10 * @param {TreeNode} root
11 * @return {void} Do not return anything, modify root in-place instead.
12 */
13var flatten = function (root) {
14  let iter = root
15  while (iter) {
16    if (iter.left) {
17      let last = iter.left
18      while (last.right) last = last.right
19      last.right = iter.right
20      iter.right = iter.left
21      iter.left = null
22    }
23    iter = iter.right
24  }
25}