Question

I’m trying to figure out how to write a code which takes an input from 0 to any positive integer, that will return a string of 0 for when zero is entered, 10 when 1 is entered, 1110 for when 2 is entered, 3110 for when 3 is entered and so on, this is saying that when input 0 occurs output is 0, then when 1 is input it looks at the input for 0 and reads it as ‘one zero’ and prints 10, the for 2 reads input 1 as ‘one one and one zero’ and prints 1110, and so on and so forth. I have an idea of what to do but it’s too vague to translate into code. When I posted this I didn’t know what it was called but since then I found that it was the look and see sequence, and my issue is that I can’t use iteration, nor can I use the built-in len() or string.append() function.

Answer 1

If you can’t use any iteration, then you need to use recursion with a stop at 0. It will look something like this:

def whatever(input):
    """
    >>> whatever(0)
    '0'
    >>> whatever(1)
    '10'
    >>> whatever(2)
    '1110'
    >>> whatever(3)
    '3110'
    >>> whatever(4)
    '132110'
    >>> whatever(5)
    '1113122110'
    """
    def looksay(input, result):
        if not input:
            return result
        else:
            left, right = input[0], input[1:]
            if not result:
                result = '1' + left
            else:
                left_result, count, right_result = result[:-2], int(result[-2]), result[-1]
                if left == right_result:
                    result = left_result + str(count + 1) + right_result
                else:
                    result = result + '1' + left
            return looksay(right, result)
    def helper(number, result):
        if number == 0:
            return result
        else:
            return helper(number - 1, looksay(result, ''))
    return helper(input, '0')

if __name__ == '__main__':
    import doctest
    doctest.testmod()