菜肴制作：拓扑排序

#include<cstdio>
#include<cstring>
#include<queue>
const int N=1e5+5;
using namespace std;
int n,m,num_bian,to[N],nxt[N],head[N],in[N],ans[N];
void add(int x,int y){
    to[++num_bian]=y,nxt[num_bian]=head[x],head[x]=num_bian,in[y]++;
}
void work(){
    scanf("%d%d",&n,&m);
    priority_queue<int>q;
    memset(head,0,sizeof(head));
    memset(in,0,sizeof(in));
    num_bian=0;ans[0]=0;
    for(int i=1,x,y;i<=m;++i)scanf("%d%d",&x,&y),add(y,x);
    for(int i=1;i<=n;++i)if(!in[i])q.push(i);
    while(!q.empty()){
        int x=q.top();q.pop();//printf("%d\n",x);
        ans[++ans[0]]=x;
        for(int i=head[x],y;i;i=nxt[i]){
            y=to[i];--in[y];
            if(!in[y])q.push(y);
        }
    }
    if(ans[0]!=n)puts("Impossible!");
    else{
        for(int i=ans[0];i;--i)printf("%d ",ans[i]);puts("");
    }
}
int main(){
    int T;scanf("%d",&T);
    while(T--)work();
    return 0;
}