TheAlgorithms-C-Plus-Plus/Graph/Topological-Sort.cpp

#include <iostream>
#include <vector>
#include <algorithm>
  using namespace std;

int n , m; // For number of Vertices (V) and number of edges (E)
vector< vector<int> > G;
vector<bool> visited;
vector<int> ans;

void dfs(int v) {
  visited[v] = true;
  for (int u : G[v]) {
    if (!visited[u])
      dfs(u);
  }
  ans.push_back(v);
}
 
void topological_sort() {
  visited.assign(n, false);
  ans.clear();
  for (int i = 0; i < n; ++i) {
    if (!visited[i])
      dfs(i);
  }
  reverse(ans.begin(), ans.end());
}
int main(){
  cout << "Enter the number of vertices and the number of directed edges\n";
  cin >> n >> m;
  int x , y;
  G.resize(n , vector<int>());
  for(int i = 0 ; i < n ; ++i) {
    cin >> x >> y;
    x-- , y--; // to convert 1-indexed to 0-indexed
    G[x].push_back(y);
  }
  topological_sort();
  cout << "Topological Order : \n";
  for(int v : ans) {
    cout << v + 1 << ' '; // converting zero based indexing back to one based.
  }
  cout << '\n';
  return 0;
}