DFS (Depth-first search)

#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <algorithm>
#include <unordered_map>
#include <set>
#include <unordered_set>

using namespace std;

void DFS(vector<vector<int>>& djacencyMatrix, int startVertex) {  // a Depth-first search
  stack<int> q;
  q.push(startVertex);
  while (!q.empty()) {
    auto a = q.top();
    cout << a << endl;
    q.pop();
    for (int i = 0; i < djacencyMatrix.size(); i++) {
      if (djacencyMatrix[a][i] == 1) {
        q.push(i);
      }
    }
  }
}

int main()
{
  size_t vrtcsN = 9;

  vector<vector<int>> adjacencyMatrix(vrtcsN, std::vector<int>(vrtcsN));

  adjacencyMatrix[0][1] = 1;
  adjacencyMatrix[0][2] = 1;
  adjacencyMatrix[1][3] = 1;
  adjacencyMatrix[1][4] = 1;
  adjacencyMatrix[1][5] = 1;
  adjacencyMatrix[2][6] = 1;
  adjacencyMatrix[2][7] = 1;
  adjacencyMatrix[7][8] = 1;

  /*   EXAMPLE TREE:       (it's guaranteed that there are no cycles in example)
            0
          /   \
        1       2
      / | \    /  \
     3  4  5   6   7
                   |
                   8
  */

  DFS(adjacencyMatrix, 0);

  // *result*: 0 2 7 8 6 1 5 4 3

}