BZOJ 4010 [HNOI2015] 菜肴制作

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反向图+拓扑序
本题证法详见黄学长博客。

#include <cstdio>#include <iostream>#include <cstdlib>#include <algorithm>#include <queue>#include <cstring>using namespace std ;const int N=100010;int D,n,m;typedef struct EDGE{    int to,next;    EDGE (){        to=next=0;    }    EDGE (int a,int b){        to=a,next=b;    }}E;E edge[N];int head[N],cnt;int ind[N];priority_queue <int> q;int ans[N],lens,vis[N];inline void E_add (int u,int v){    edge[++cnt]=EDGE (u,head[v]);    head[v]=cnt;    ind[u]++;}void init (){    cin >>D;}void readin (){    int i,j,k;    scanf ("%d %d",&n,&m);    for (i=1;i<=m;i++){        scanf ("%d %d",&j,&k);        E_add (j,k);    }}void work (){    int i,now,p;    memset (ans,0,sizeof(ans));    lens=0;    for (i=1;i<=n;i++){        if (ind[i]==0) q.push(i);    }    while (!q.empty ()) {        now=q.top ();        q.pop ();        ans[++lens]=now;        for (p=head[now];p;p=edge[p].next){            ind[edge[p].to]--;            if (ind[edge[p].to]==0) q.push (edge[p].to);        }    }    if (lens!=n) {        printf ("Impossible!\n");        return ;    }    else {        for (i=n;i>=1;i--) printf ("%d ",ans[i]);        printf ("\n");    }}int main (){    init ();    int i;    for (i=1;i<=D;i++){        memset (ind,0,sizeof (ind));        memset (head,0,sizeof(head));        cnt=0;        readin ();        work ();    }    return 0;}

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