UVA 10763 Foreign Exchange

建立两个数组同时存储原学校与目标学校。分别按优先原学校和优先目标学校排序，一一配对，验查是否可行。

#include <iostream>
#include <algorithm>
using namespace std;

struct node {
    int x,y;
}a[500010],b[500010];

bool cmp1 (node x,node y){
    if ((x.x<y.x)||(x.x==y.x&&x.y<y.y))
        return true ;
    return false ;
}
bool cmp2 (node x,node y){
    if ((x.y<y.y)||(x.y==y.y&&x.x<y.x))
        return true ;
    return false ;
}

int main (){
    int n;
    while (cin>>n&&n){
        for (int i=0;i<n;i++){
            cin>>a[i].x>>a[i].y;
            b[i].x=a[i].x;
            b[i].y=a[i].y;
        }
        sort (a,a+n,cmp1);
        sort (b,b+n,cmp2);
        int flag=1;
        for (int i=0;i<n;i++){//cout<<i<<":"<<a[i].x<<" "<<a[i].y<<"  "<<b[i].x<<" "<<b[i].y<<endl;
            if (a[i].x==b[i].y&&a[i].y==b[i].x)
                continue ;
            flag=0;break ;
        }
        if (flag)
            cout<<"YES"<<endl;
        else cout<<"NO"<<endl;
    }
    return 0;
}