【LeetCode】面试题32-1. 从上到下打印二叉树

题目:

思路:

该题目应该属于Easy类型，利用队列实现层次遍历或者广度优先搜索(BFS)。这里利用list的头插入功能模拟队列。

代码:

Python

# 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 levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[int]
        """
        res = []
        q = []
        q.append(root)
        while q:
            tmp = q.pop()
            if tmp is not None:
                res.append(tmp.val)
                if tmp.left is not None:
                    q.insert(0, tmp.left)
                if tmp.right is not None:
                    q.insert(0, tmp.right)
        return res

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