How to make this more time efficient??

Question

#include <iostream>
#include<math.h>
using namespace std;
int lcm(int a,int b)
{
for(int i=max(a,b) ; ;i++)
{
if(i%a==0 && i%b==0)
return i;
}
}

int main() {
// your code goes here

int n;
cin>>n;
int a[n];
for(int i=0 ;i<n ;i++)
cin>>a[i];

int maxa=0;

for(int i= 0 ; i<n ;i++)
{
for(int j=i+1 ;j<n ;j++)
{
maxa=max(maxa,lcm(a[i],a[j]));
}
}

cout<<maxa;
return 0;
}

Answer 1

Just notice that lcm of a ant b can be found more efficiently as a result of a * b / greatest common factor as like code below

int gcf(int n1, int n2)
{
  int div;
  if (n1 == n2)  return n1;
  int d = n1 - n2;
  if (d < 0) {
    d = -d;  div = gcf(n1, d);
  } else
    div = gcf(n2, d); 
  return div;
}

lcm(int a, int b){
return a * b / gcf(a, b);
}