# 107.BinaryTreeLevelOrderTraversalII
// https://leetcode-cn.com/problems/binary-tree-level-order-traversal-ii/
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[][]}
*/
var levelOrderBottom = function(root) {
var ans = [];
if (!root) {
return ans;
}
var nodes = [root];
while(nodes.length) {
var layer = [];
var nextNodes = [];
nodes.forEach((node) => {
layer.push(node.val);
if(node.left) nextNodes.push(node.left);
if(node.right) nextNodes.push(node.right);
})
ans.push(layer);
nodes = nextNodes;
}
return ans.reverse();
};