Project Euler Solution: Problem 3

Largest prime factor

Problem 3

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

What is the largest prime factor of the number 600851475143 ?

source link: https://projecteuler.net/problem=3

The time comlexity of my last solution is too large.

I think the shink the size of iteration condition number will optimize that.

 

Here is my original code:

#include <iostream>
#include <vector>
#include <string>
#include <cmath>
#include <iostream>

using namespace std;

int main()
{
    long long int const size = 600851475143;
    vector<int> pr;
    pr.push_back(2);
    int maxPr = 2;
    for (long int i = 3; i < sqrtl(size); i++) {
        bool isPr = true;
        for (long int cnt = 1; pr[cnt] < sqrtl(pr.back()); cnt++) {
            if (i % pr[cnt] == 0) {
                isPr = false;
                break;
            }
        }

        if (isPr) {
            pr.push_back(i);
            if (size % i == 0) {
                maxPr = i;
                cout << maxPr << endl;
            }

        }

        return 0;
    }
}