Please tell me why its wrong (LCM & GCD )

Question

Question : Given an array of n numbers, find LCM of it.

Since LCM(a,b) = a*b / GCD(a,b), here is my original code:

class GFG {

      // the simple 2 integers recursive to find their GCD.

    static int getGcd(int a, int b){
        while(a != b){
            if(a >b){
                a = a-b;
            }else{
                b= b-a;
            }
        }
        return a;
    }

    // find GCD in an array that has more than two integers.

    static int Gcd(int[] newArray){

     int gcd = newArray[0];
       for(int i=1; i<newArray.length; i++){
        gcd = getGcd(gcd,newArray[i]);
     }

        return gcd;
    }

    static int Lcm(int[] newArray){
        int multi =1;
        for(int i=0; i< newArray.length; i++){
            multi = multi* newArray[i];
        }
        return (multi/gcd);
    }

    public static void main (String[] args) {
        int[] newArray = { 2, 7, 3, 9, 4 };
        System.out.println(Gcd(newArray));
        System.out.println(Lcm(newArray));
    }
}

But when I run this code, it shows some error:

prog.java:33: error: cannot find symbol
        return (multi/gcd);
                      ^
  symbol:   variable gcd

I don't know how to fix it. Please help me to correct my code... Thanks!!!

Answer 1

There is no gcd defined in the Lcm() function. The gcd last defined was in Gcd() function, while this is not a global variable Lcm() cannot use it.

Maybe you mean this?

static int Lcm(int[] newArray){
    int multi =newArray[0];
    int gcd = 0;
    for(int i=1; i< newArray.length; i++){
        gcd = getGcd(multi, newArray[i]);
        if(gcd == 1) {
            multi = multi * newArray[i];
        }else {
            multi = multi * newArray[i] / gcd;
        }
    }
    return multi;
}

Use this could generate the result. You could just have a think about this. We start from 2, multi is 2, and the next value is 7. The gcd for 2 and 7 is 1, so the lcd will be 14. Then we use 14 to compare 3, gcd is also 1, so just multi them is 42. Then use 42 compare 9, we found that 9 have the gcd with 42 is 3, so we use 42/3 is 14, then use 14 and 9, gcd is 1, give multi 14x9 is 126. Then use 126 and 4, the gcd is 2, so multi is 126/2 = 63, and 63 and 4 gcd is 1, so finally multi is 63x4 is 252.

If you have a look of any two numbers, no matter is [3,7],[50,5],[20,10],[100,10000],[52,57],[3,81], the lcm is always a*b/gcd. In this case we could get the answer.