【leetCode】Binary Tree Zigzag Level Order Traversal python实现

最新推荐文章于 2020-10-20 18:58:34 发布

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本文介绍了一种二叉树的锯齿形层序遍历算法，通过层次遍历的方式对偶数层节点进行反向处理，实现了二叉树节点值的特殊遍历顺序。

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Binary Tree Zigzag Level Order Traversal

原题链接

Binary Tree Zigzag Level Order Traversal

实现原理解析

层次遍历即可，对于偶数层的做反向

python代码实现

import copy

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

class Solution(object):
    def __init__(self):
        self.result = []

    def zigzagLevelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root is None:
            return []
        else:
            rootLevel =[root]
            self.result.append(rootLevel)
            self.levelSearch(rootLevel)
        for i in xrange(len(self.result)):
            if i%2 == 1:
                self.result[i].reverse()

            self.result[i] = [each.val for each in self.result[i]]
        return self.result


    def levelSearch(self, upLevelNodes):
        """
        :param upLevelNodes:
        :return:
        """
        ret = []
        if len(upLevelNodes) == 0:
            self.result.pop()
            return
        for eachNode in upLevelNodes:
            if eachNode.left is not None:
                ret.append(eachNode.left)
            if eachNode.right is not None:
                ret.append(eachNode.right)
        if len(ret) == 0:
            return
        self.result.append(ret)
        self.levelSearch(ret)