#include <iostream>
#include <vector>

using namespace std;

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 {

public:
  void dfs(const TreeNode *root, vector<int> &res) {
    if (root == nullptr)
      return;
    dfs(root->left, res);
    res.push_back(root->val);
    dfs(root->right, res);
  }

  vector<int> inorderTraversal(TreeNode *root) {
    vector<int> res;
    dfs(root, res);
    return res;
  }
};

int main(void) {
  TreeNode *root = new TreeNode(1);
  root->right = new TreeNode(2);
  root->right->left = new TreeNode(3);
  for (const auto &i : Solution().inorderTraversal(root)) {
    cout << i << endl;
  }
  return 0;
}