reverse-words-in-a-string.py

"""

151. Reverse Words in a String
Medium

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

 

Example 1:

Input: s = "the sky is blue"
Output: "blue is sky the"
Example 2:

Input: s = "  hello world  "
Output: "world hello"
Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:

Input: s = "a good   example"
Output: "example good a"
Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
 

Constraints:

1 <= s.length <= 104
s contains English letters (upper-case and lower-case), digits, and spaces ' '.
There is at least one word in s.
 

Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?

"""

# V0
# IDEA : py string op
class Solution(object):
    def reverseWords(self, s):
        _s = s.strip().split(" ")
        _s_list = [x for x in _s if len(x) > 0][::-1]
        return " ".join(_s_list)

# V1 
# http://bookshadow.com/weblog/2014/10/16/leetcode-reverse-words-string/
class Solution:
    # @param s, a string
    # @return a string
    def reverseWords(self, s):
        words = s.split()
        words.reverse()
        return " ".join(words)
        
# V2
# Time:  O(n)
# Space: O(n)
class Solution(object):
    # @param s, a string
    # @return a string
    def reverseWords(self, s):
        return ' '.join(reversed(s.split()))