leetcode 树的锯齿形状遍历

二叉树的锯齿形层次遍历

 

 

给定一个二叉树，返回其节点值的锯齿形层次遍历。（即先从左往右，再从右往左进行下一层遍历，以此类推，层与层之间交替进行）。

例如：
给定二叉树 [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

返回锯齿形层次遍历如下：

[
  [3],
  [20,9],
  [15,7]
]

我的想法是把树的每一层存起来，然后 技术层次的结点顺序翻转一下

 # Definition for a binary tree node.
 # class TreeNode:
 #     def __init__(self, x):
 #         self.val = x
 #         self.left = None
 #         self.right = None

 class Solution:
     def zigzagLevelOrder(self, root):
         """
         :type root: TreeNode
         :rtype: List[List[int]]
         """
         if root is None:
             return []
         res = [[root]]
         res_int = [[root.val]]
         i = 0
         while i < len(res):
             cur = res[i]
             nLayer = []
             nLyayer_int = []
             for n in cur:
                 if n.left is not None:
                     nLayer.append(n.left)
                     nLyayer_int.append(n.left.val)
                 if n.right is not None:
                     nLayer.append(n.right)
                     nLyayer_int.append(n.right.val)
             if nLayer:
                 res.append(nLayer)
                 if i % 2 == 0:
                     nLyayer_int.reverse()
                 res_int.append(nLyayer_int)

             i += 1

         return res_int