TwoRepeatingElementsByIndex.java

public class TwoRepeatingElementsByIndex {
    //this solution will work only if all the numbers are in the range of 1 to n and are >0
    //navigate the array if number is x then multiply the A[x] by -1.
    //If A[x] is already negative, then it means we are visiting it second time, means it is repeated.
    public static void twoRepeating(int [] A, int n){
        System.out.print("Repeated Elements are: ");
        for (int i = 0; i <A.length ; i++) {
            if(A[Math.abs(A[i])]<0)
                System.out.print(Math.abs(A[i]) + " ");
            else
                A[Math.abs(A[i])] = A[Math.abs(A[i])] * -1;
        }
    }
    public static void main(String[] args) {
        int [] A = {1,4,5,6,3,2,5,2};
        int n = 6;
        twoRepeating(A, n);
    }
}