[LeetCode 199] Binary Tree Right Side View (递归的层数）

题目内容

199 Binary Tree Right Side View
Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

For example:
Given the following binary tree,

1 <—
/ \
2 3 <—
\ \
5 4 <—

You should return [1, 3, 4].

Credits:
Special thanks to @amrsaqr for adding this problem and creating all test cases.
题目原文

题目简述

从上到下写出二叉树每层最右侧节点对应的数值

题目分析

按层次递归，并将层数作为递归变量使每层只记录一个数值，从右至左遍历则使每层右边节点最先遍历，该节点数值即可在本层唯一记录。

代码示例

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    void recursion(vector<int> &res,TreeNode *root,int level)    {        if(root==NULL) return;        if(res.size()<level) res.push_back(root->val);        recursion(res,root->right,level+1);        recursion(res,root->left,level+1);    }    vector<int> rightSideView(TreeNode *root)    {        vector<int> res;        recursion(res,root,1);        return res;    }};