#include <iostream>
#include <vector>
#include "Exercises.h"

// Gives multiple of all multiples of 3 or 5 under given number.
int Ex1(int in) {
    int out = 0;

    for (int i = 3; i < in; i += 3) out += i;
    for (int i = 5, t = 1; i < in; i += 5, t++) {
        if (t == 3) t = 0; 
        else out += i; 
    }
    return out;
}

// Gives multiple of all even fibonacci sequence values under given number
int Ex2(int in) {
    int v1 = 0, v2 = 1, f = 0, out = 0;
    while (true) {
        // calc fibonacci value
        f = v1 + v2;
        v1 = v2;
        v2 = f;

        // stop if fibonacci value over max
        if (in < f) break;
        // skip if uneven
        if ((f & 0b1) == 1) continue;

        // sum
        out += f;
    }
    return out;
}

/*
Works but needs to be optimised for large number: 600851475143
*/
// Gives biggest prime factor of given number
unsigned long long Ex3(unsigned long long in) {
    vector<unsigned long long> primes = { 2 };
    unsigned long long biggest_prime = -1;

    for (unsigned long long num = 2; num <= in; num++)
    {
        // Find prime
        bool isPrime = true;
        for (auto prime : primes)
        {
            isPrime = num % prime != 0;
            if (!isPrime) break;
        }
        if (!isPrime) continue;
        primes.push_back(num);

        // Is number factor of input, if not go to next number.
        if (in % num != 0) continue;

        // Save current prime as biggest prime and promote other factor as new max.
        biggest_prime = num;
        in = in / num;
    }
    return biggest_prime;
}