Zju1015 Fishing Net

　　弦图判定

　　代码

 #include<cstdio>
 #include<queue>
 #define mp make_pair
 #define fi first
 #define sc second
 using namespace std;
 const int N = ;
 int n,m,a,b,i,j;
 int dp,p[N],pre[N],tt[N],o,vis[N],sum[N],id[N],ID[N];
 priority_queue<pair<int,int> > Q;
 void link(int x,int y)
 {
     dp++;pre[dp]=p[x];p[x]=dp;tt[dp]=y;
 }
 int main()
 {
     scanf("%d%d",&n,&m);
     for (i=;i<=m;i++)
     {
         scanf("%d%d",&a,&b);
         link(a,b);
         link(b,a);
     }
     for (i=;i<=n;i++)
     Q.push(mp(,i));
     o=n;
     while (!Q.empty())
     {
         int x=Q.top().fi;
         int y=Q.top().sc;
         Q.pop();
         if (vis[y]) continue;
         if (x<sum[y]) continue;
         ID[y]=o;
         id[o--]=y;
         vis[y]=;
         i=p[y];
         while (i)
         {
             if (!vis[tt[i]])
             {
                 sum[tt[i]]++;
                 Q.push(mp(sum[tt[i]],tt[i]));
             }
             i=pre[i];
         }
     }
     for (i=;i<=n;i++) vis[i]=;

     for (j=;j<=n;j++)
     {
         int x=id[j],cnt1=,cnt2=,mi=0x37373737,y=;
         i=p[x];
         while (i)
         {
             if (ID[tt[i]]>j)
             {
                 if (ID[tt[i]]<mi) mi=ID[tt[i]],y=tt[i];
                 vis[tt[i]]=;cnt1++;
             }
             i=pre[i];
         }

         if (y)
         {
             i=p[y];
             while (i)
             {
                 if (vis[tt[i]]) cnt2++;
                 i=pre[i];
             }
         }
         if ((cnt1!=cnt2+)&&(y))
         {
             printf("Imperfect");
             return ;
         }
         i=p[x];
         while (i)
         {
             vis[tt[i]]=;
             i=pre[i];
         }
     }
     printf("Perfect");
 }