题目描述

输入样例

3 3
1 2
2 3
1 3

输出样例
···
1 2 3
···

参考代码

#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 d[N], q[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++)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);d[b]++;}if (topsort()){for (int i = 0; i < n; i++) printf("%d ", q[i]);puts("");}else puts("-1");return 0;
}