题目链接：有向图的拓扑排序

#include <cstring>
#include <iostream>
#include <algorithm>using namespace std;const int N = 100010;int n, m;
int h[N], e[N], ne[N], idx;int q[N], d[N];void add(int a, int b)
{e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}bool topsort()
{int hh = 0, tt = -1;for(int i = 1; i <= n; i++){// 如果入度为0，添加到队列中if(!d[i]) 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()
{cin >> n >> m;memset(h, -1, sizeof h);for(int i = 0; i < m; i ++){int a, b;cin >> a >> b;add(a, b);// b的入度+1d[b] ++;}if(topsort()){for(int i = 0; i < n; i++){cout << q[i] << ' ';}}else cout << "-1" << endl;return 0;
}