拓扑排序的原理和宽度优先搜索差不多

#include <iostream>
#include <cstring>
#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++)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];if(--d[j]==0){q[++tt]=j;}}}return tt==n-1;
}int main(void)
{scanf("%d%d", &n,&m);memset(h, -1, sizeof h);while (m -- ){int a,b;scanf("%d%d",&a,&b);add(a,b);d[b]++;}if(topsort()){for(int i=0;i<n;i++)printf("%d ",q[i]);}else puts("-1");return 0;
}