Checking element-wise whether two arrays share at least one element in Java

Question

I'm trying to find an efficient way in Java to check whether two arrays have at least one element in common element-wise. So this means [1, 2, 2, 3] and [2, 3 ,5 ,6] would give False, whereas [1, 2, 2, 3] compared with [5, 2, 1, 5] would give True. Currently I loop over the elements, and break out of the loop once one of the elements is equal. Is there a more efficient way?

Answer 1

Dont think that you can do better than O( min(array1.length, array2.length) )

There are micro optimizations you can do such as loop unrolling ( https://en.wikipedia.org/wiki/Loop_unrolling ) although you may want to think carefully before going down this path.

Answer 2

You can compare element by element two arrays and return when you find a match with true, else return false.

public class ArrayCheck {

    public static void main(String[] arg){
        int[] a = {1, 2, 2, 3};
        int[] b = {2, 3 ,5 ,6};
        int[] c = {5, 2, 1, 5};

        System.out.println("Result " + elementWiseCompare(a,b));
        System.out.println("Result " + elementWiseCompare(a,c));
    }

    public static boolean elementWiseCompare(int[] a, int [] b){

        for(int i = 0; i < a.length && i < b.length; i++){
            if (a[i] == b[i]){
                return true;
            }
        }
        return false;
    }
}

Outputs:

Result false Result true