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:

 1 #include <iostream>
 2 #include <vector>
 3 #include <string>
 4 #include <cmath>
 5 #include <iostream>
 6
 7 using namespace std;
 8
 9 int main()
10 {
11     long long int const size = 600851475143;
12     vector<int> pr;
13     pr.push_back(2);
14     int maxPr = 2;
15     for (long int i = 3; i < sqrtl(size); i++) {
16         bool isPr = true;
17         for (long int cnt = 1; pr[cnt] < sqrtl(pr.back()); cnt++) {
18             if (i % pr[cnt] == 0) {
19                 isPr = false;
20                 break;
21             }
22         }
23
24         if (isPr) {
25             pr.push_back(i);
26             if (size % i == 0) {
27                 maxPr = i;
28                 cout << maxPr << endl;
29             }
30
31         }
32
33         return 0;
34     }
35 }