1 #include <iostream> 2 #include <map> 3 #include <cstring> 4 #include <cstdio> 5 6 using namespace std; 7 8 int father[100010]; 9 int num[100010]; 10 11 int main() 12 { 13 int a,b; 14 while(true) 15 { 16 int flag=1; 17 int time=1; 18 for(int i=1;i<=100000;i++) 19 father[i]=i; 20 for(int i=1;i<=100000;i++) 21 num[i]=1; 22 while(cin>>a>>b) 23 { 24 if(a==0&&b==0) 25 break; 26 if(a==-1&&b==-1) 27 goto F1; 28 time++; 29 int fa=a; 30 int fb=b; 31 while(fa!=father[fa]) 32 { 33 fa=father[fa]; 34 } 35 while(fb!=father[fb]) 36 { 37 fb=father[fb]; 38 } 39 int t1=a; 40 while(t1!=fa) 41 { 42 int tmp=father[t1]; 43 father[t1]=fa; 44 t1=tmp; 45 } 46 int t2=b; 47 while(t2!=fb) 48 { 49 int tmp=father[t2]; 50 father[t2]=fb; 51 t2=tmp; 52 } 53 if(fa==fb) 54 flag=0; 55 else 56 { 57 father[fb]=fa; 58 num[fa]+=num[fb]; 59 num[fb]=0; 60 } 61 } 62 if(flag) 63 { 64 flag=0; 65 for(int i=1;i<=100000;i++) 66 { 67 if(num[i]==time) 68 { 69 flag=1; 70 } 71 } 72 } 73 if(flag) 74 cout<<"Yes"<<endl; 75 else 76 cout<<"No"<<endl; 77 } 78 F1: 79 return 0; 80 }