CSC401-Recursive

Purpose

The purpose of this request is to assess your understanding of

Recursive functions
Recursive thinking
Next week, we will continue with topics in Chapter 10.

Submission

Include your full name as a comment on the first line of your Python program.
Submit (upload) to the dropbox one file labeled as YourName_HW8.py

Problem

All of the following problems use recursion. So, you are cannot use any types of loops, string processing functions other than slicing, global variables, remove, replace, etc.

Problem 1

Write a recursive function stars(n) that takes an input a nonnegative integer and generates the pattern of stars shown below:

>>> stars(4)
****
***
**
*
*
**
***
****
>>>

Your function should produce a pattern for any nonnegative integer.

Problem 2

Write a recursive function alt(s,t) that takes as input two strings and mixes string s and t with alternating characters from each string.. Check that s and t have the same length; if not, return immediately.

>>> alt('abc```de', 'vwxyz')
avbwcxdyez
>>>
>>> alt('hello', 'world')
hweolrllod
>>>

Problem 3

Write a recursive function check(s) that take a string representing a password as input and returns all the characters that are digits ( 0 -9)

>>> check('abc')
>>> check('1abc2efg')
2 1
>>> check('a0b8nd79')
9 7 8 0

Problem 4

Write a recursive function prompt() that asks the user to enter a password. If the user simply hits return without entering anything, the function should prompt again, until the user enters a string. The string is then returned (not printed). Do not use any type of loop.

>>> prompt()
Enter password:
Enter password:
Enter password:
Enter password:
Enter password:abc1ghki9$%funny
'abc1ghki9$%funny'