107.二叉树的层序遍历-ii.js

/*
 * @lc app=leetcode.cn id=107 lang=javascript
 *
 * [107] 二叉树的层序遍历 II
 */

// @lc code=start
/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrderBottom = function(root) {
  let res = []
  if (root) {
    let queue = [root]
    while (queue.length) {
      let len = queue.length
      const temp = []
      for (let i = 0; i < len; i++) {
        const node = queue.shift()
        temp.push(node.val)
        node.left && queue.push(node.left)
        node.right && queue.push(node.right)
      }
      res.unshift(temp)
    }
  }
  return res
}
// @lc code=end