Problem 3

problem

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 600851475143 ?

Code

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

static vector<long long> factorsList;

bool isPrime(int n)
{
    if(n < 2) return false;

    for(int i = 3; i*i <= n; i+=2)
        if(n%i == 0) return false;

    return true;
}

int main()
{
    long long num = 600851475143;

    for (long long i = 3; i < num; i+=2)
    {
        if (num % i == 0)
        {
            if (isPrime(num/i))
            {
                cout << num/i << endl;
                break;
            }
        }
    }

}