记录入度数

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+10;
int val[N],ne[N],h[N],idx;
queue<int> q;
vector<int> ans;
int degree[N];
int n,m;

void add(int a,int b)
{
    val[idx] = b;
    ne[idx] = h[a];
    h[a] = idx++;
}

bool topsort()
{
    for(int i = 1;i<=n;i++)
    {
        if(degree[i] == 0)q.push(i);
    }

    while(q.size())
    {
        int t = q.front();
        ans.push_back(t);
        q.pop();
        for(int i = h[t];~i;i = ne[i])
        {
            int j = val[i];
            if(--degree[j] == 0)q.push(j);
        }
    }
    return ans.size() == n;
}
int main()
{
    cin>>n>>m;
    memset(h, -1, sizeof h);
    while(m--)
    {
        int a,b;
        cin>>a>>b;
        add(a,b);
        degree[b]++;
    }
    if(topsort())
    {
        for(int i = 0;i<ans.size();i++)cout<<ans[i]<<" ";
    }
    else puts("-1");
    return 0;
}