BZOJ 4010 拓扑排序+heap

//By SiriusRen
#include <queue>
#include <cstdio>
#include <cstring>
using namespace std;
const int N=200050;
int cases,n,m,xx,yy,du[N],first[N],next[N],v[N],w[N],tot,ans[N],top;
void add(int x,int y){v[tot]=y,next[tot]=first[x],first[x]=tot++;}
priority_queue<int>pq;
int main(){
    scanf("%d",&cases);
    while(cases--){
        memset(first,-1,sizeof(first)),tot=top=0;
        memset(du,0,sizeof(du));
        scanf("%d%d",&n,&m);
        for(int i=1;i<=m;i++){
            scanf("%d%d",&xx,&yy);
            add(yy,xx),du[xx]++;
        }
        for(int i=1;i<=n;i++)if(!du[i])pq.push(i);
        while(!pq.empty()){
            int t=pq.top();pq.pop();
            ans[++top]=t;
            for(int i=first[t];~i;i=next[i]){
                du[v[i]]--;
                if(!du[v[i]])pq.push(v[i]);
            }
        }
        if(top!=n){puts("Impossible!");continue;}
        for(int i=top;i;i--)printf("%d ",ans[i]);puts("");
    }
}