[LeetCode] 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]
]

这个题目非常明显的适用BFS, 从root, 依次将每一层append进入ans里, 只是要注意的就是如果判断哪个是在哪一层呢, 这里用到的方法是利用size of queue, 每次得到的size就是该层的数目, 每层用一个temp list去存每一层的元素, 结束之后append进入ans中. 

1. Constraints  1) tree 可以为empty, 所以edge case 为root == None

2. Ideas

    BFS   T: O(n)     S: O(n)    n is number of nodes in the tree

3. code

import collections
class Solution:def levelOrder(self, root):""":type root: TreeNode:rtype: List[List[int]]"""if not root: return []ans, queue = [], collections.deque([root])while queue:size, level = len(queue), []for _ in range(size):node = queue.popleft()level.append(node.val)if node.left:queue.append(node.left)if node.right:queue.append(node.right)ans.append(level)return ans

4. Test cases

1) None => []

2) [1] => [[1]]

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]
]

转载于:https://www.cnblogs.com/Johnsonxiong/p/9261520.html

[LeetCode] 102. Binary Tree Level Order Traversal_Medium tag: BFS相关推荐

LeetCode 102. Binary Tree Level Order Traversal--递归，迭代-Python，Java解法
题目地址: Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to ...
LeetCode: 102. Binary Tree Level Order Traversal
题目 Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to rig ...
Leetcode 102. Binary Tree Level Order Traversal（二叉树的层序遍历）
Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, ...
LeetCode 102. Binary Tree Level Order Traversal
原题 Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to rig ...
LeetCode: 107. Binary Tree Level Order Traversal II
题目 Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from l ...
LeetCode 107. Binary Tree Level Order Traversal II
LeetCode 107. Binary Tree Level Order Traversal II Solution1:我的答案比102那道题多了一行代码... /*** Definition f ...
102. Binary Tree Level Order Traversal
题目 Binary Tree Level Order Traversal 层次遍历二叉树链接 Given a binary tree, return the level order traversa ...
Leet Code OJ 102. Binary Tree Level Order Traversal [Difficulty: Easy]
题目: Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to ri ...
LeetCode之Binary Tree Level Order Traversal 层序遍历二叉树
题目描述: Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to ...

[LeetCode] 102. Binary Tree Level Order Traversal_Medium tag: BFS

[LeetCode] 102. Binary Tree Level Order Traversal_Medium tag: BFS相关推荐

最新文章

热门文章