Kahn's algorithm [TopoSort]

#include <bits/stdc++.h>
using namespace std;

const int N=1e5+10;

struct Node
{
    vector<int> adj;
    int indeg;
    Node()
    {
        indeg=0;
    }
} g[N];

int n, m, topo[N];

bool Kahn ()
{
    int idx=0;
    queue<int> q;
    for (int i=1;i<=n;i++) if (!g[i].indeg) q.push(i);

    while (!q.empty())
    {
        int v=q.front();
        q.pop();
        topo[++idx]=v;

        for (int i=0;i<g[v].adj.size();i++)
        {
            int u=g[v].adj[i];
            g[u].indeg--;
            if (!g[u].indeg) q.push(u);
        }
    }

    if (idx==n) return true; //svi cvorovi stavljeni
    return false; //postoji ciklus
}

int main()
{
    scanf ("%d%d", &n, &m);
    for (int i=0;i<m;i++)
    {
        int a, b;
        scanf ("%d%d", &a, &b);
        g[a].adj.push_back(b);
        g[b].indeg++;
    }

    if (Kahn()) for (int i=1;i<=n;i++) printf ("%d ", topo[i]);
    else printf ("-1");

    return 0;
}