力扣-二叉树的层序遍历

题链接：leetcode-cn.com/problems/bi…

解题 与层序遍历的思路相同，最后将得到的list反转就好

 * 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) {
    if(!root) return []
    const queue = [root]
    const result = []
    while(queue.length) {
        const temp = []
        for(let i = queue.length; i> 0; i--) {
            const n = queue.shift()
            temp.push(n.val)
            n.left && queue.push(n.left)
            n.right && queue.push(n.right)
        }
        result.push(temp)
    }
    return result.reverse()
};