#include<iostream>
#include<map>
#include<set>
using namespace std;
int main()
{
int n;
while(scanf("%d",&n) && n)
{
map<int, int> a, b;
set<int> ans;
bool flag = false;
for (int i = 0; i < n; i++)
{
int x, y;
cin >> x >> y;
a[x] ++; b[y] ++;
ans.insert(x); ans.insert(y);
}
set<int>::iterator it;
for (it = ans.begin(); it !=ans.end(); it++)
{
if(a[*it] != b[*it])
{
flag = true;
break;
}
}
if(flag) cout << "NO" << endl;
else cout << "YES" << endl;
}
}
UVA - 10763 Foreign Exchange【map】
最新推荐文章于 2020-08-23 16:07:01 发布