PAIR2021 -Editorial

editorial
1

Question Link

Difficulty
Easy

Prerequisite
Implementation

Explanation
Just check for each bottle, can I pair it with another. In this task can pass absolutely any solutions.

Author's Solution 
#include<bits/stdc++.h>
#define ll long long
#define io ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
using namespace std;
#define N 100000
#define mod 1000000007
    
template <typename T>
void print(T x){cout<<x<<"\n";}
template <typename T1, typename T2>
void print2(T1 x,T2 y){cout<<x<<" "<<y<<"\n";}
template <typename T1, typename T2,typename T3>
void print3(T1 x, T2 y,T3 z){cout<<x<<" "<<y<<" "<<z<<"\n";}
    
int main()
{
    io;
    ll test_case;
    //cin>>test_case;
    test_case=1;
    while(test_case--)
    {
        ll n;
        cin>>n;
        ll a[n],b[n],c[1001]={0};
        for(int i=0;i<n;i++)
        {
            cin>>a[i]>>b[i];
            c[b[i]]++;
        }
        ll res=0;
        for(int i=0;i<n;i++)
        {
            c[b[i]]--;
            if(c[a[i]]==0)
            res++;
    
            c[b[i]]++;
        }
        print(res);
    }
}