FZU-1924+判断环/DFS/BFS

dfs：

 /*
 dfs
 */
 #include<stdio.h>
 #include<string.h>
 #include<stdlib.h>
 #include<algorithm>
 #include<iostream>
 #include<queue>
 #include<map>
 #include<stack>
 #include<set>
 #include<math.h>
 using namespace std;
 typedef long long int64;
 //typedef __int64 int64;
 typedef pair<int64,int64> PII;
 #define MP(a,b) make_pair((a),(b))
 const int maxn = ;
 const int inf = 0x7fffffff;
 const double pi=acos(-1.0);
 const double eps = 1e-;

 int vis[ maxn ];
 struct Edge{
     int u,next;
 }edge[ maxn<< ];
 int cnt,head[ maxn ];
 void init(){
     memset( vis,-,sizeof( vis ) );
     cnt = ;
     memset( head,-,sizeof( head ) );
 }
 void addedge( int a,int b ){
     edge[ cnt ].u = b;
     edge[ cnt ].next = head[ a ];
     head[ a ] = cnt++;
 }

 bool flag;
 int ans;
 void dfs( int cur ){
     if( flag ) return ;
     vis[ cur ] = ;
     for( int i=head[ cur ];i!=-;i=edge[i].next ){
         int nxt = edge[i].u;
         if(nxt == ans){
             flag = true;
             return;
         }
         if(vis[ nxt ] == )continue;
         if( flag )return;
         dfs( nxt );
     }
 }

 int main(){
     int T;
     scanf("%d",&T);
     int Case = ;
     while( T-- ){
         int n,m;
         scanf("%d%d",&n,&m);
         int edge_a,edge_b;
         scanf("%d%d",&edge_a,&edge_b);
         int x,y;
         init();
         while( edge_a-- ){
             scanf("%d%d",&x,&y);
             x++,y++;
             y += n;
             addedge( x,y );
         }
         while( edge_b-- ){
             scanf("%d%d",&x,&y);
             x++,y++;
             x += n;
             addedge( x,y );
         }
         flag = false;

         for( int i=;i<=n;i++ ){
             memset(vis,,sizeof(vis));
             ans = i;
             dfs(i);
             if(flag)break;
             /*
             if( flag==false&&vis[i]==-1 ){
                 dfs( i,-1 );
             }
             */
         }
         printf("Case %d: ",Case ++ );
         if( flag ) printf("Possible\n");
         else printf("Impossible\n");
     }
     return ;
 }