题解 | #【模板】拓扑排序#

#include <cstring>
#include <iostream>
using namespace std;

const int N = 200010;
int h[N], idx, e[N], ne[N];
int q[N], d[N];
int n, m;
void add(int a, int b){
    e[idx] = b;
    ne[idx] = h[a];
    h[a] = idx ++;
}

bool topSort(){
    int tt = -1, hh = 0;
    for(int i = 1; i <= n; i ++){
        if(d[i] == 0) q[++ tt] = i;
    }
    while(hh <= tt){
        int t = q[hh ++];
        for(int i = h[t]; i != -1; i = ne[i]){
            int j = e[i];
            d[j] --;
            if(d[j] == 0) q[++ tt] = j;
        }
    }
    return tt == n - 1;
}

int main() {
    memset(h, -1, sizeof h);
    cin >> n >> m;
    while(m --){
        int a, b;
        cin >> a >> b;
        add(a, b);
        d[b] ++;
    }
    if(topSort()){
        for(int i = 0; i < n; i ++){
            cout << q[i] << endl;
            if(i != n - 1)  cout << " ";
        }
    }
    else puts("-1");
    return 0;
}