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151. Reverse Words in a String

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Basant Babu Bhandari
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2 min read

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 <= 10<sup>4</sup>

  • s contains English letters (upper-case and lower-case), digits, and spaces ' '.

  • There is at least one word in s.

Solution:

class Solution(object):
    def reverseWords(self, s):
        length = len(s)
        word_positions = []  # To store start and end indices of words

        i = 0
        # Iterate through the string to identify word boundaries
        while i < length:
            # Skip leading spaces
            while i < length and s[i] == ' ':
                i += 1
            if i == length:
                break

            start = i  # Start of the word

            # Move to the end of the word
            while i < length and s[i] != ' ':
                i += 1
            end = i - 1  # End of the word

            # Store the start and end indices of the word
            word_positions.append((start, end))

        result = []
        # Reverse the order of the words and build the result string
        for start, end in reversed(word_positions):
            word = s[start:end + 1]
            result.append(word)

        return ' '.join(result)
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