elements = [1,2,3,4,5,6]
combinations = []
k = 3

def get_combinations(elem_idx, current_set):
    
    if elem_idx == len(elements):
        return

    new_set = current_set[:]
    new_set.append(elements[elem_idx])

    if len(new_set) == k:
        combinations.append(new_set)

    get_combinations(elem_idx+1, current_set)
    get_combinations(elem_idx+1, new_set)


get_combinations(0, [])

print(combinations)