rightside.cc

/**
 * 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 {
  map<int, vector<int>> levels;
public:
  void helper(const TreeNode *node, int height) {
    if (node == nullptr) {
      return;
    }
    levels[height].push_back(node->val);
    helper(node->left, height + 1);
    helper(node->right, height + 1);
  }

  vector<int> rightSideView(const TreeNode* root) {
    helper(root, 0);
    vector<int> ans;
    ans.reserve(levels.size());
    for (const auto &[_, row] : levels) {
      ans.push_back(row.back());
    }
    return ans;
  }
};