reverse_words.py

'''
This problem is taken from Stanford's CS 9: Problem-Solving for the CS Technical Interview.

Question statement:
Reverse all the words in a string of words and spaces / tabs 
while preserving the word order and spacing.
Example
'moo cow bark dog' -> 'oom woc krab god'

Potential pitfalls:
Don't reverse the entire string -- preserve the word ordering and the spaces.
We make no guarantee about how many spaces / tabs there are between words, 
so you can't split (using the .split() method) and then reverse the words individually.

My solution:
Start with current word to be None.
Iterate over each character in the string.
	+ if it's space/tabs:
		+ if the current word is not None, reverse it and add it to result.
		+ add current character to the result.
	+ else:
		+ if the previous character is space/tab, make it the first character of current word.
		+ else, add the current character to the current word

'''

def reverse_string(string):
	if len(string) <= 1:
		return string
	return string[-1] + reverse_string(string[:-1])

def reverse_words(string):
	curr_word = ''
	results = ''
	for char in string:
		if char == ' ' or char == '\t':
			if not curr_word == '':
				results += reverse_string(curr_word)
				curr_word = ''
			results += char
		else:
			curr_word += char
	results += reverse_string(curr_word)
	return results

assert reverse_words('moo cow  bark dog') == 'oom woc  krab god'
assert reverse_words('moo	') == 'oom	'
assert reverse_words('	 moo moo') == '	 oom oom'
assert reverse_words(' 	') == ' 	'