Right view of Binary tree

• Time : $O(n)$
• Space : $O(h)$

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
void dfs(TreeNode* node, int depth, vector<int>& res) {
    if(!node) return;
    if(res.size() == depth) res.push_back(-1);
    res[depth] = node->val;
    dfs(node->left, depth + 1, res);
    dfs(node->right, depth + 1, res);
}
vector<int> Solution::solve(TreeNode* A) {
    vector<int> res;
    dfs(A,0,res);
    return res;
}