java 8 Collections.sort(ar); int count = 0; int temp = 0; for(int i = 0; i < n; i++){

        if(temp == ar.get(i)){
            temp = 0;
            continue;
        }
        temp = ar.get(i);
        if((i + 1) < n && temp == ar.get(i + 1)){
            count++;
        }
    }
    return count;