note:coded using while and for loops check both programs.

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Actually, in the general method it takes too much time since we check until the minimum of the both numbers and find the maximum/greatest common divisor. but in this EUCLID DIVISION OR LONG DIVISION METHOD the number of steps is minimized. so,this is less complex and faster than that algorithm.

using while loop

class Main
{
public static int gcd(int A,int B)
{
    int a=A;
    int b=B;
    int a_,b_;
while(a!=0)
{
     a_= b%a;
     b_=a;
    a = a_;
    b = b_;
}
return b;
}
public static void main(String args[])
{
    int res= gcd(6,15);
    System.out.println("gcd is "+ res);
}

}

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gcd is 3

using for loop

class Main
{
public static int gcd(int A,int B)
{
    int a=A;
    int b=B;
    int a_,b_;
for( ;a!=0; )
{
    a_=b%a;
    b_=a;
    a=a_;
    b=b_;
}
return b;
}
public static void main(String args[])
{
    int res= gcd(6,15);
    System.out.println("gcd is "+ res);
}
}

[Success] Your code was executed successfully

gcd is 3