[LeetCode]102 二叉树的层次遍历

题目描述

给定一个二叉树，返回其按层次遍历的节点值。 （即逐层地，从左到右访问所有节点）。

例如:
给定二叉树:[3,9,20,null,null,15,7],

  3
 / \
9  20
  /  \
 15   7

返回其层次遍历结果：

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

代码

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

class Solution:
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root == None:
            return []
        stack = [root]
        res = []
        while stack != []:
            x = []
            for item in stack:
                x.append(item.val)
            res.append(x)
            tmp = []
            for item in stack:
                if item.left != None:
                    tmp.append(item.left)
                if item.right != None:
                    tmp.append(item.right)
            stack = tmp
        return res