Foreign Exchange (UVA - 10763)

#include <iostream>
#include <bits/stdc++.h>
#define maxn 500002
using namespace std;

int N1[maxn];
int N2[maxn];

int main()
{
    int n;
    int a,b;
    while(cin>>n&&n!=0)
    {
        int ok = 1;
        for(int i = 0;i<n;i++)
        {
            cin>>N1[i]>>N2[i];
        }
        if(n%2)
        {
            cout<<"NO"<<endl;
            continue;
        }
        sort(N1,N1+n);
        sort(N2,N2+n);
        for(int i = 0;i<n;i++)
        {
            if(N1[i]!=N2[i])
            {
                ok = 0;
                break;
            }
        }
        if(ok) cout<<"YES"<<endl;
        else  cout<<"NO"<<endl;
    }
    return 0;
}

如果是强行只能两间学校之间互相交换，而单单只保证学校的学生人数不变的话，上面的解题是不够严谨的，修改了一下答案应该是下面这样：

#include <iostream>
#include <bits/stdc++.h>

using namespace std;


int main()
{
    int n;
    int a,b;
    while(cin>>n&&n!=0)
    {
        int ok = 1;
        map<pair<int,int>,int>mp;
        for(int i = 0;i<n;i++)
        {
            cin>>a>>b;
            pair<int,int>p = make_pair(a,b);
            mp[p]++;
        }
        if(n%2)
        {
            cout<<"NO"<<endl;
            continue;
        }
        for(auto it = mp.begin();it != mp.end();it++)
        {
            auto p1 = it->first;
            a = p1.first;
            b = p1.second;
            p1.first = b;
            p1.second = a;
            if(mp[p1] != it->second)
            {
                cout<<"NO"<<endl;
                ok = 0;
                break;
            }
            
        }
        if(ok) cout<<"YES"<<endl;
    }
    return 0;
}