Project Euler Problem 3

问题：

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

What is the largest prime factor of the number 600851475143 ?

答案：6857

#include
#include

int main(void)
{
    long int n = 600851475143L;
    int lastFactor = 2;

    if(n%2==0){
        lastFactor = 2;
        n = n/2;
        while(n%2==0)
            n = n/2;
    }   
    else
        lastFactor = 1;
    int factor = 3;

    int maxFactor = sqrt(n);
    while(n>1 && factor<=maxFactor){
        if(n%factor==0){
            n = n/factor;
            lastFactor = factor;
            while(n/factor==0)
                n = n/factor;
            maxFactor = sqrt(n);
        }
        factor += 2;
    }

    if(n==1)
        printf("%d\n", lastFactor);
    else
        printf("%d\n", n);

    return 0;
}