拓扑排序
#include <bits/stdc++.h>
using namespace std;const int N = 1e5 + 10;int e[N], ne[N], h[N], idx;
int n, m, d[N];
int q[N];void add(int a,int b){e[idx] = b, ne[idx] = h[a], h[a] = idx ++;
}bool top_sort(){int hh = 0, tt = -1;for(int i = 1;i <= n; i++) {if(d[i] == 0) q[++ tt] = i;}while(hh <= tt){auto 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(){// 单链表, h初始化为-1, 用于存储图时, 对于每一个头节点都要初始化为-1, 要不然会超时memset(h, -1 , sizeof h);cin >> n >> m;for(int i = 1; i <= m; i++){int a,b;cin >> a >> b;add(a , b);d[b] ++;}if(top_sort()){for(int i = 0;i < n; i++) cout << q[i] << " ";}else cout << "-1" << "\n";return 0;
}