1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 #include <vector> 5 6 using namespace std; 7 8 vector<int> used; 9 int father[101000]; 10 11 int main() 12 { 13 int time=1; 14 while(true) 15 { 16 for(int i=0;i<=101000;i++) 17 { 18 father[i]=i; 19 } 20 int flag=1; 21 int x,y; 22 used.clear(); 23 while(scanf("%d%d",&x,&y)!=EOF) 24 { 25 if(x==-1&&y==-1) 26 goto F; 27 if(!(x==0&&y==0)) 28 { 29 if(father[y]==y) 30 { 31 int fx=x; 32 while(fx!=father[fx]) 33 { 34 fx=father[fx]; 35 } 36 if(fx==y) 37 flag=0; 38 father[y]=fx; 39 used.push_back(x); 40 used.push_back(y); 41 while(x!=fx) 42 { 43 int tmp=father[x]; 44 father[x]=fx; 45 x=tmp; 46 } 47 } 48 else 49 flag=0; 50 } 51 else 52 { 53 if(used.empty()) 54 printf("Case %d is a tree. ",time); 55 else 56 { 57 int f=used[0]; 58 int ff; 59 while(f!=father[f]) 60 f=father[f]; 61 for(int i=1;i<used.size();i++) 62 { 63 ff=used[i]; 64 while(ff!=father[ff]) 65 { 66 ff=father[ff]; 67 } 68 if(ff!=f) 69 { 70 flag=0; 71 break; 72 } 73 } 74 if(flag) 75 printf("Case %d is a tree. ",time); 76 else 77 printf("Case %d is not a tree. ",time); 78 } 79 time++; 80 break; 81 } 82 } 83 } 84 F: 85 return 0; 86 }