combinations in java
private void helper(List<int[]> combinations, int data[], int start, int end, int index) {
if (index == data.length) {
int[] combination = data.clone();
combinations.add(combination);
}
else if (start <= end) {
data[index] = start;
helper(combinations, data, start + 1, end, index + 1);
helper(combinations, data, start + 1, end, index);
}
}