199. Binary Tree Right Side View.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    void preorder(TreeNode* node, int level, vector<int> & ans){
        if(node == nullptr) return;
        
        if(ans.size() < level) ans.push_back(node->val);
            
        preorder(node->right, level + 1, ans);
        preorder(node->left, level + 1, ans);
    }
    
public:
    vector<int> rightSideView(TreeNode* root) {
        vector<int> ans;
        preorder(root, 1, ans);
        return ans;
    }
};