779A - Pupils Redistribution - CodeForces Solution

#include <iostream>
#include <algorithm>
#include <map>
#include <math.h>

using namespace std;

int main()
{
    int n;
    cin >> n;
    int a[n];
    int b[n];
    map<int, int> ca;
    map<int, int> cb;
    for(int i = 0; i < n; i++)
    {
        cin >> a[i];
        ca[a[i]]++;
    }
    for(int i = 0; i < n;i++)
    {
        cin >> b[i];
        cb[b[i]]++;
    }
    int dis = 0;
    int pos = 0;
    for(int i = 1; i <= 5; i++)
    {
        int tmp = ca[i] + cb[i];
        if(tmp % 2 == 1)
        {
            cout << -1;
            return 0;
        }
        dis += ca[i] - cb[i];
        if(ca[i] - cb[i] > 0)
            pos += (ca[i] - cb[i]);
    }
    if(dis == 0)
        cout << pos/2;
    else
        cout << -1;
}