151. Reverse Words in a String

Question

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?

Prakash Sellathurai · Accepted Answer

class Solution:
    def reverseWords(self, s: str) -> str:
        # reverse the s
        #  us etwo piinter to reverse the individual words

def reverse(s, i , j):
            while i < j:
                s[i], s[j] = s[j],s[i]
                i += 1
                j-=1
        s = list(s)
        n = len(s)
        reverse(s,0, n -1)
        i = 0
        res = []
        while i < n:
            j = i 
            while j < n and s[j] != ' ':
                j+=1
            reverse(s, i, j-1)
            word = "".join(s[i:j])
            if word:
                res.append(word)
            while j< n and s[j] == ' ':
                j+=1
            i = j    
        return " ".join(res)