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.

Example 4:

Input: s = "  Bob    Loves  Alice   "
Output: "Alice Loves Bob"

Example 5:

Input: s = "Alice does not even like bob"
Output: "bob like even not does Alice"

 

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, message: str) -> str:
        result = ""
        current = len(message) - 1

        while current >= 0:
            # move to the start of word
            checkpoint = current + 1
            while current >= 0 and message[current] != " ":
                current -= 1

            for temporal in range(current + 1, checkpoint):
                result += message[temporal]

            # move spaces
            while current >= 0 and message[current] == " ":
                current -= 1

            # add spaces
            if current != -1 and len(result):
                result += " "

        return result