reverse-words-in-a-string-ii.py

# Time: O(n)
# Space:O(1)
#
# Given an input string, reverse the string word by word.
# A word is defined as a sequence of non-space characters.
# 
# The input string does not contain leading or trailing spaces
# and the words are always separated by a single space.
# 
# For example,
# Given s = "the sky is blue",
# return "blue is sky the".
# 
# Could you do it in-place without allocating extra space?
#

class Solution(object):
    def reverseWords(self, s):
        """
        :type s: a list of 1 length strings (List[str])
        :rtype: nothing
        """
        def reverse(s, begin, end):
            for i in xrange((end - begin) / 2):
                s[begin + i], s[end - 1 - i] = s[end - 1 - i], s[begin + i]

        reverse(s, 0, len(s))
        i = 0
        for j in xrange(len(s) + 1):
            if j == len(s) or s[j] == ' ':
                reverse(s, i, j)
                i = j + 1


if __name__ == '__main__':
    s = ['h','e','l','l','o', ' ', 'w', 'o', 'r', 'l', 'd']
    Solution().reverseWords(s)
    print s