(LeetCode) 199. Binary Tree Right Side View

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].

思路

作前序遍历，先左后右，将高度相同的节点替换前面的，就可以得到题目想要的效果。

代码

/** * 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:    vector<int> rightSideView(TreeNode* root) {        vector<int> res;        dfs(root, res);        return res;    }    void dfs(TreeNode* root, vector<int> &res){        if(root==NULL) return;        stack<pair<TreeNode*, int>> stk;        stk.push(make_pair(root,0));        TreeNode* cur = root;        int level = 0;        while(!stk.empty()){            cur = stk.top().first;            level = stk.top().second;            stk.pop();            if(level>=res.size()) res.push_back(cur->val);            if(cur->left!=NULL) stk.push(make_pair(cur->left, level+1));            if(cur->right!=NULL) stk.push(make_pair(cur->right, level+1));        }    }};