0151-reverse-words-in-a-string

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Description

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?

Solution(Python)

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)