ProjectEuler

// 001

1 #include 
     
       2  3 using namespace std; 4  5 int main() 6 { 7     int sum = 0; 8     for (int i = 3; i < 1000; ++ i) { 9         if (i % 3 == 0 || i % 5 == 0) {10             sum += i;11         }12     }13     cout << sum << endl;14 15     return 0;16 }
     

//002

1 #include 
     
       2  3 using namespace std; 4  5 int main() 6 { 7     int num1 = 1, num2 = 2; 8     int temp = 0; 9     int sum = 0;10     while (num2 < 4000001) {11         if (num2 % 2 == 0) {12             sum += num2;13         }14         temp = num1 + num2;15         num1 = num2;16         num2 = temp;17     }18     cout << sum << endl;19 20     return 0;21 }
     

// 003

1 #include 
     
       2 #include 
      
        3  4 using namespace std; 5  6 bool isPrime(int); 7  8 int main() 9 {10     double sq = sqrt(600851475143.0);11     int num = sq;12     for (int i = num; i > 1; -- i) {13         if (600851475143 % i == 0 && isPrime(i)) {14             cout << i << endl;15             break;16         }17     }18 19     return 0;20 }21 22 bool isPrime(int num)23 {24     if (num < 2) return false;25     for (int i = 2; i <= sqrt((double)num); ++ i) {26         if (num % i == 0) {27             return false;28         }29     }30     return true;31 }