1145 Hashing - Average Search Ti

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

bool isprime(int inp)
{
    if (inp <= 0) return false;
    for (int i = 2; i <=inp/2; i++)
    {
        if (inp%i==0)
        {
            return false;
        }
    }
    return true;
}

int main()
{
    int Msize, N, M;
    cin >> Msize >> N >> M;
    while(isprime(Msize) == false) Msize++;

    //cout << Msize << endl;
    vector<int> v(Msize);
    fill(v.begin(), v.end(), -1);
    int a,b;
    bool flag = false;
    for (int i = 0; i < N; i++)
    {
        cin >> a;
        for (int j = 0; j < Msize; j++)
        {
            b=(a + j * j) % Msize;
            if (v[b] == -1)
            {
                v[b] = a;
                flag = true;
                break;
            }
        }
        if (flag==false)
        {
            cout << a << " cannot be inserted." << endl;
        }
        flag = false;
    }

    double ans = 0.0;
    for (int i = 0; i < M; i++)
    {
        cin >> a;
        int cnt = 1;
        for (int j = 0; j < Msize; j++)
        {
            b = (a + j * j) % Msize;
            if (v[b] == a||v[b]==-1) break;
            cnt++;
        }
        ans += cnt;
    }
    printf("%.1lf\n", ans / M);
    system("pause");
    return 0;
}