HackerEarth Studious Amit and His New College problem solution

In this HackerEarth Studious Amit and His New College problem solution Amit has been awarded as the most meritorious student award in school. He is proud of it and decides to further improve his performance in his new college. He has to take N courses. The courses are labelled from 1 to N. Some courses might have prerequisites. For example, to take Data Structure course, one needs to take C Programming course first. There are M such pair denoting the course and it’s corresponding prerequisite course which Amit needs to take first in order to successfully finish that particular course.

Given the number of courses he needs to take and a list of prerequisites pair, find out whether it is possible for Amit to finish all the courses and once again prove his mettle.

#include<bits/stdc++.h>
using namespace std;
#define N 1000010
int visited[N];
bool f;
vector<int> g[N];
void dfs(int u)
{
  visited[u] = 1;
  for(auto v : g[u])
  {
    if(!visited[v])
      dfs(v);
    else if(visited[v] == 1)  //cycle found
      f = true;
  }
  visited[u] = 2;
}
int main()
{
  int tc;
  scanf("%d",&tc);
  while(tc--)
  {
    f = false;
    int n,m;
    scanf("%d%d",&n,&m);
    for(int i = 1;i <= n;i++)
    {
      g[i].clear();
      visited[i] = 0;
    }
    for(int i=0;i<m;i++)
    {
      int u,v;
      scanf("%d%d",&u,&v);
      g[u].push_back(v);
    }
    for(int i = 1;i <= n; i++)
    {
      if(!visited[i])
      {
        dfs(i);
        if(f)
          break;
      }
    }
    if(f)
      printf("0n");
    else
      printf("1n");
  }
  return 0;
}