def triangle_helper(n, limit, buffer):
    # base case: we're out of X's to print
    if n == 0:
        print(buffer)
        return

    # for every possible number of X's to print at this level, starting with as many as possible
    for i in reversed(range(1, min(limit, n) + 1)):
        # print the X's, then print that many X's less on the next levels
        triangle_helper(n - i, i, '%s%s\n' % (buffer, 'X' * i))


def triangle(n):
    triangle_helper(n, n, '')


triangle(2)