Leetcode 103. Binary Tree Zigzag Level Order Traversal

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最新推荐文章于 2024-01-19 11:15:23 发布

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本文介绍了一种特殊的二叉树遍历方式——锯齿形层序遍历，即从左到右再从右到左交替进行层级遍历。通过使用队列实现算法，针对每个层级节点值的收集和反转处理，最终得到锯齿形遍历结果。

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Given a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from left to right, then right to left for the next level and alternate bet
ween).

For example:
Given binary tree [3,9,20,null,null,15,7],
在这里插入图片描述
return its zigzag level order traversal as:
[[3],[20,9],[15,7]]

# 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]]
        """
        res = []
        if not root:
            return res
        
        queue = [root]
        
        while queue:
            level = []
            for _ in range(len(queue)):
                curr = queue.pop(0)
                level.append(curr.val)
                if curr.left:
                    queue.append(curr.left)
                if curr.right:
                    queue.append(curr.right)
            if len(res) % 2 == 1:
                level = level[::-1]
            res.append(level)
        
        return res