ProjectEuler 003题

1 //题目：The prime factors of 13195 are 5, 7, 13 and 29.
2 //What is the largest prime factor of the number 600851475143 ?

 1 #include<iostream>
 2 using namespace std;
 3 int main() {
 4     long long N = 600851475143;//int和long都为32位，long long 为64位
 5     int i;
 6     bool isPrime(long long num);
 7     long long res;
 8     for(i=2; i<=N;i++){
 9         while(isPrime(i) && N%i == 0.0){
10             N = N/i;
11             res = i;
12         }
13     }
14     cout << res << endl;
15     system("pause");
16     return 0;
17 }
18 bool isPrime(long long num){
19     int i=0;
20     for(i = 2; i*i <= num; i++){
21
22         if(num%i == 0.0)
23             return false;
24     }
25     return true;
26 }