https://projecteuler.net/problem=19

#include <bits/stdc++.h>
using namespace std;

const int N = 1000000;

bool isLeap(int n)
{
    if(n%400==0) return true;

    if(n%100==0) return false;

    if(n%4==0) return true;

    return false;
}

int main()
{
    map< int, int > days;
    days[1] = days[3] = days[5] = days[7] = days[8] = days[10] = days[12] = 3;
    days[4] = days[6] = days[9] = days[11] = 2;
    days[2] = 0;
    int curr = 2;
    int ans = 0;
    for(int i=1901; i<=2000; i++) {
        for(int j=1; j<=12; j++) {
            if(curr%7==0) {
                // cout << i << " " << j << "\n";
                ans++;
            }
            // cout << i << " " << j << " " << curr << "\n";
            int dd = days[j];
            if(j==2 && isLeap(i)) {
                // cout << "Leap year: " << i << "\n";
                dd++;
            }

            curr += dd;
            // curr %= 8;
        }
    }
    cout << ans << '\n';
}