kahn's algorithm

// KAHN'S ALGORITHM FOR TOPSORT ORDERING
// IT USES THE CONCEPT OF INDEGREE
#include<bits/stdc++.h>

using namespace std;

vector<int> ar[10001];
vector<int> ans;
int inDegree[10001];

void kahn(int n)
{
    queue<int> q;
    for(int i=1;i<=n;++i)
       if(inDegree[i]==0)
         q.push(i);

    while(!q.empty())
    {
        int curr = q.front();
        ans.push_back(curr);

        q.pop();

        for(int child : ar[curr])
        {
            inDegree[child]--;
            if(inDegree[child]==0)
               q.push(child);
        }
    }
}

int main()
{
    int n , m , a , b;

    cout<<"Enter the number of vertices and number of edges: ";
    cin>>n>>m;
    for(int i=1;i<=n;++i)    inDegree[i] = 0;
    cout<<"\nEnter the values of graph:\n";
    while(m--)
     cin>>a>>b , ar[a].push_back(b) , inDegree[b]++;

    kahn(n);

    cout<<"\nTop sort order is:\n";
    for(int i=0;i<ans.size();++i)
      cout<<ans[i]<<" ";

    return 0;
}