I'm trying to do a little exercise: for a given array and a given difference k, return the unique pairs of the array which difference is k.

The logic is not too complicated: Get a set from the array to make sure items are unique, get unique pairs with two loops, if difference == k, increment the counter.

 public static int countPairsWithDiff(int[] numbers, int difference) {
        var uniqueNumbers = Set.of(numbers);
        var count = 0;
        var ln = uniqueNumbers.size();
        for (int i = 0; i < ln ; i++) {
            for (int j = i; j < ln; j++) {
                if (Math.abs(i-j) == difference) {
                    count++;
                }
            } 
        }

        return count;
    }

The .size() method evaluates to 0 (edit: 1) however. Why is this?