How to reduce program execution time?

Question

Programming

Is there a code how to reduce the program execution time so that it is less than one second?

#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
freopen("input.txt","r",stdin);
freopen("output.txt","w",stdout);
  int S=0,Smax=0,n,i,k;
  cin>>n;
  for(int i=1;i <= n;i++)
  {
   S=0;
   for(int j=1;j <= n;j++)
   {
    if(i%j == 0)
    S=S+j;
    if(S > Smax){Smax=S;k=i;}
   }
}
cout<<k;
return 0;
}

Answer 1

Rewrite the algorithm. And to help you with this, first I would like to understand what this algorithm does. At first glance, this is a search for a number from 1 to n, the sum of divisors of which is maximum, right?

Answer 2

At first glance, why not take it out
if(S > Smax){Smax=S;k=i;}
of the second cycle? And that turns out at each pass there is a check.