Leetcode 102. Binary Tree Level Order Traversal

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

Link: 102. Binary Tree Level Order Traversal

Examples:

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]
]

思路: 给定二叉树的root节点，按层返回值，每层一个list. 逐层遍历，保存每层所有节点的val到一个list, 所有的非None左右节点到一个list，即下一层待遍历的所有节点，直到节点list为空。

class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """
        if root is None: return []
        nodes = [root]
        vals = []
        while nodes:
            temp = []
            tempNodes = []
            for n in nodes:
                temp.append(n.val)
                if not n.left is None:
                    tempNodes.append(n.left)
                if not n.right is None:
                    tempNodes.append(n.right)
            vals.append(temp)
            nodes = tempNodes
        return vals

日期: 2021-01-13 It has been long time that I didn't solve problems in leetcode because of preparing a paper experiments, but all these are excuses, so I should return back and stick to do it. New year, this is one of my targets.