UVA 10763 Foreign Exchange

 1 #include <iostream>
 2 #include <algorithm>
 3 using namespace std;
 4 
 5 struct node {
 6     int x,y;
 7 }a[500010],b[500010];
 8 
 9 bool cmp1 (node x,node y){
10     if ((x.x<y.x)||(x.x==y.x&&x.y<y.y))
11         return true ;
12     return false ;
13 }
14 bool cmp2 (node x,node y){
15     if ((x.y<y.y)||(x.y==y.y&&x.x<y.x))
16         return true ;
17     return false ;
18 }
19 
20 int main (){
21     int n;
22     while (cin>>n&&n){
23         for (int i=0;i<n;i++){
24             cin>>a[i].x>>a[i].y;
25             b[i].x=a[i].x;
26             b[i].y=a[i].y;
27         }
28         sort (a,a+n,cmp1);
29         sort (b,b+n,cmp2);
30         int flag=1;
31         for (int i=0;i<n;i++){//cout<<i<<":"<<a[i].x<<" "<<a[i].y<<"  "<<b[i].x<<" "<<b[i].y<<endl;
32             if (a[i].x==b[i].y&&a[i].y==b[i].x)
33                 continue ;
34             flag=0;break ;
35         }
36         if (flag)
37             cout<<"YES"<<endl;
38         else cout<<"NO"<<endl;
39     }
40     return 0;
41 }