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void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
  if (r != nullptr) {
    m[x][y].insert(r->val);
    dfs(r->left, x - 1, y + 1, m);
    dfs(r->right, x + 1, y + 1, m);
  }
}
vector<vector<int>> verticalTraversal(TreeNode* r, vector<vector<int>> res = {}) {
  map<int, map<int, set<int>>> m;
  dfs(r, 0, 0, m);
  for (auto itx = m.begin(); itx != m.end(); ++itx) {
      res.push_back(vector<int>());
      for (auto ity = itx->second.begin(); ity != itx->second.end(); ++ity) {
          res.back().insert(end(res.back()), begin(ity->second), end(ity->second));
      }
  }
  return res;
}

prog.cpp:1:10: error: variable or field ‘dfs’ declared void
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
          ^~~~~~~~
prog.cpp:1:10: error: ‘TreeNode’ was not declared in this scope
prog.cpp:1:20: error: ‘r’ was not declared in this scope
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                    ^
prog.cpp:1:23: error: expected primary-expression before ‘int’
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                       ^~~
prog.cpp:1:30: error: expected primary-expression before ‘int’
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                              ^~~
prog.cpp:1:37: error: ‘map’ was not declared in this scope
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                     ^~~
prog.cpp:1:41: error: expected primary-expression before ‘int’
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                         ^~~
prog.cpp:1:46: error: ‘map’ was not declared in this scope
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                              ^~~
prog.cpp:1:50: error: expected primary-expression before ‘int’
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                                  ^~~
prog.cpp:1:55: error: ‘set’ was not declared in this scope
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                                       ^~~
prog.cpp:1:59: error: expected primary-expression before ‘int’
 void dfs(TreeNode* r, int x, int y, map<int, map<int, set<int>>> &m) {
                                                           ^~~

Standard output is empty