CheckDuplicates.java

import java.util.Arrays;

public class CheckDuplicates {
    public static void main(String[] args) {
        int[] values = { 8, 5, 9, 8, 6, 13, 33, 1, 98, 12, 8, 1 };
        System.out.println(Arrays.toString(findDuplicates(values)));
    }

    public static int[] findDuplicates(int[] values) {
        int buffSize = 10;
        int[] duplicates = new int[buffSize];
        Arrays.sort(values);
        for (int i = 1, j = 0; i < values.length; i++) {
            if (values[i] == values[i - 1]) {
                duplicates[j++] = values[i];
                while (values[i] == values[i - 1]) {
                    i++;
                }
            }
            if (j == buffSize - 1) {
                duplicates = growArray(duplicates, 2);
                buffSize = duplicates.length;
            }
        }
        return clipArray(duplicates);
    }

    public static int[] growArray(int[] arr, float factor) {
        int newLength = (int)(arr.length * factor);
        int[] temp = new int[newLength];
        System.arraycopy(arr, 0, temp, 0, arr.length);
        return temp;
    }

    public static int[] clipArray(int[] arr) {
        int i = 0;
        while (i < arr.length) {
            if (arr[i] == 0) {
                break;
            } else {
                i++;
            }
        }
        return Arrays.copyOfRange(arr, 0, i);
    }
}