按层次遍历，记录下对应节点的val和所在层，然后经过一定变换得到输出。python代码如下：

# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution(object):    def zigzagLevelOrder(self, root):        """        :type root: TreeNode        :rtype: List[List[int]]        """        tmp = []        if root == None:            return tmp        tmp.append(root)        tmp_list = []        cengshu = 0        while(tmp != []):            tmp_next = []            for i in range(len(tmp)):                tmp_list.append([tmp[i].val , cengshu])                if tmp[i].left != None:                    tmp_next.append(tmp[i].left)                if tmp[i].right != None:                    tmp_next.append(tmp[i].right)            tmp = tmp_next            cengshu += 1        from collections import defaultdict        dict_new = defaultdict(list)        for i in range(len(tmp_list)):            dict_new[tmp_list[i][1]].append(tmp_list[i][0])        final_return = []        for i in range(len(dict_new.values())):            if i % 2 == 0:                final_return.append(dict_new.values()[i])            else:                t = dict_new.values()[i]                t.reverse()                final_return.append(t)        return final_return