http://www.lightoj.com/volume_showproblem.php?problem=1168
1 #include <cstdio> 2 #include <cstring> 3 #include <algorithm> 4 using namespace std; 5 #define N 1005 6 struct{ 7 int y,next; 8 }ee[10*N]; 9 struct{ 10 int a,b; 11 }mes[10*N]; 12 int link[N],dfn[N],low[N],pos[N],stack[N],t,st,bct,ind,in[N],out[N]; 13 bool vis[N],instack[N],inn[N]; 14 void init() 15 { 16 memset(link,0,sizeof(link)); 17 memset(inn,0,sizeof(inn)); 18 memset(out,0,sizeof(out)); 19 memset(vis,0,sizeof(vis)); 20 memset(instack,0,sizeof(instack)); 21 memset(in,0,sizeof(in)); 22 t=0,st=0,bct=0,ind=0; 23 } 24 void tarjan(int rt) 25 { 26 low[rt]=dfn[rt]=++ind; 27 vis[rt]=instack[rt]=1; 28 stack[++st]=rt; 29 for(int i=link[rt];i;i=ee[i].next){ 30 if(!vis[ee[i].y]){ 31 tarjan(ee[i].y); 32 low[rt]=min(low[rt],low[ee[i].y]); 33 } 34 else if(instack[ee[i].y]){ 35 low[rt]=min(low[rt],dfn[ee[i].y]); 36 } 37 } 38 if(low[rt]==dfn[rt]){ 39 bct++; 40 while(1){ 41 int c=stack[st]; 42 pos[c]=bct; 43 instack[c]=0; 44 st--; 45 if(c==rt)break; 46 } 47 } 48 } 49 void insert(int a,int b) 50 { 51 ee[++t].y=b; 52 ee[t].next=link[a]; 53 link[a]=t; 54 } 55 void rebuild(int m) 56 { 57 memset(link,0,sizeof(link)); 58 t=0; 59 for(int i=1;i<=m;i++){ 60 if(pos[mes[i].a]!=pos[mes[i].b]){ 61 insert(pos[mes[i].a],pos[mes[i].b]); 62 out[pos[mes[i].a]]++; 63 in[pos[mes[i].b]]++; 64 } 65 } 66 } 67 int main() 68 { 69 int tt,cas=1; 70 scanf("%d",&tt); 71 while(tt--){ 72 int n,m=0,k; 73 init(); 74 inn[0]=1; 75 scanf("%d",&n); 76 for(int i=1;i<=n;i++){ 77 scanf("%d",&k); 78 while(k--){ 79 int a,b; 80 scanf("%d%d",&a,&b); 81 insert(a,b); 82 inn[a]=1; 83 inn[b]=1; 84 m++; 85 mes[m].a=a,mes[m].b=b; 86 } 87 } 88 for(int i=0;i<1000;i++) 89 if(!vis[i]&&inn[i]) 90 tarjan(i); 91 if(bct==1){ 92 printf("Case %d: YES ",cas++); 93 continue; 94 } 95 rebuild(m); 96 97 if(in[pos[0]]!=0||out[pos[0]]==0){ 98 printf("Case %d: NO ",cas++); 99 continue; 100 } 101 int cnt1=0,cnt2=0,cnt3=0; 102 for(int i=1;i<=bct;i++){ 103 if(in[i]==0&&out[i]==1){ 104 cnt1++; 105 } 106 else if(in[i]==1&&out[i]==0){ 107 cnt2++; 108 } 109 else if(in[i]==1&&out[i]==1) 110 cnt3++; 111 } 112 if(cnt1==1&&cnt2==1&&cnt1+cnt2+cnt3==bct) 113 printf("Case %d: YES ",cas++); 114 else 115 printf("Case %d: NO ",cas++); 116 } 117 return 0; 118 }