/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

void traversal(map<int, vector<int>> &mp, TreeNode* A, int level){
    if(A != NULL)
        mp[level].push_back(A->val);
    if(A->left)
        traversal(mp, A->left, level+1);
    if(A->right)
        traversal(mp, A->right, level);
}

vector<int> Solution::solve(TreeNode* A) {
    map<int, vector<int>> mp;
    traversal(mp, A, 0);
    vector<int>res;
    for(auto it: mp){
        for(auto it2 : it.second){
            res.push_back(it2);
        }
    }
    return res;
}