leetcode 103. 二叉树的锯齿形层次遍历

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题目链接：leetcode

思路：广度优先遍历，加一个标志flag判断是否转换位置

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
from collections import deque
class Solution(object):
    def zigzagLevelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        flag = 1
        if not root:return []
        q = deque()
        q.append(root)
        res = []
        while q:
            n = len(q)
            tmp = []
            for i in range(n):
                node = q.popleft()
                tmp.append(node.val)
                if node.left:q.append(node.left)
                if node.right:q.append(node.right)
            if flag==1:
                res.append(tmp)
                flag = 0
            else:
                res.append(tmp[::-1])
                flag = 1
        return res