102. Binary Tree Level Order Traversal

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

 

return its level order traversal as:

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

道理我都懂，怎么用python写！！！

# 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[List[int]]
        """
        res = []
        if not root:
            return res
        temp = [root]
        while temp:
            cur = []
            next_temp = []
            for node in temp:
                cur.append(node.val)
                if node.left:
                    next_temp.append(node.left)
                if node.right:
                    next_temp.append(node.right)
            res.append(cur)
            temp = next_temp
        return res

 思路就是用temp表示当前层节点，next_temp表示下一层节点

通过node不断访问

用cur保存每一层的结果然后添加到res结果里面