白菜刷LeetCode记-103. Binary Tree Zigzag Level Order Traversal

今天的题目是对昨天题目的加深印象，题目如下：

有了昨天的答案，今天做得就比较轻松了，代码如下：

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var zigzagLevelOrder = function(root) {
    let res = new Array();
    
    helper(root, res, 0);
    
    for(let i = 0 ; i < res.length ; i++){
        if(i%2){
            res[i].reverse();
        }
    }
    
    return res;
};

var helper = function(root, res, level){
    if(root == null)  return;
    
    if(res.length < level + 1){
        res.push([]);
    }
    
    helper(root.left, res, level + 1);
    helper(root.right, res, level + 1);
    
    res[level].push(root.val);
}