Problem 1 : Sum of Divisor of 3 and 5

Algorithm

Iterate over all multiple of 3 and 5 and populate it in a variable

Code

#include <iostream>
using namespace std;
#define n 1000
int main(){
    int i=3,sum=0;
    while(i<=1000){
        sum += i;
        i+=3;
    }
    for(i=5; i<= n; i+=5){
        sum += i;
    }
    for(i=15; i<=n; i+=15){
        sum -= i;
    }
    cout << sum;
    return 0;
}

Analysis

Time Complexity : O(n)
Space Complexity : O(1)

Reference

hackerrank