Table of Contents
Introduction
The Reverse Words in a String problem is a classic string manipulation challenge that appears frequently in coding interviews and is part of the LeetCode 75 study plan.
Given a string s, reverse the order of the words in the string.
- A word is defined as a sequence of non-space characters.
- Words are separated by one or more spaces.
- You must return a string where:
- Words are in reverse order,
- Separated by a single space,
- And there are no leading or trailing spaces.
Example 1:
Input: s = " the sky is blue "
Output: "blue is sky the"
Example 2:
Input: s = "hello world"
Output: "world hello"
Constraints:
1 <= s.length <= 10^4scontains English letters (upper/lowercase), digits, and spaces- No leading/trailing words, but may contain extra spaces
Python Solution for Reverse Words in a String
class Solution:
def reverseWords(self, s: str) -> str:
# Split the string into a list of words
words = s.split()
# Reverse the order of words
reversed_words = words[::-1]
# Join the reverse words to form the final result
reversed_string = ' '.join(reversed_words)
return reversed_string
Step-by-Step Explanation
Step 1: Split the String into Words
words = s.split()
- The
split()method:- Automatically removes extra spaces,
- And splits the string by whitespace.
- Result is a list of words.
Example:
s = " the sky is blue "
words = ['the', 'sky', 'is', 'blue']
Step 2: Reverse the List of Words
reversed_words = words[::-1]
- The slicing syntax
[::-1]reverses the list in Python.
Output:
['blue', 'is', 'sky', 'the']
Step 3: Join the Words with a Single Space
reversed_string = ' '.join(reversed_words)
- Combines the reversed words into a single string with one space between each word.
Final Output:
"blue is sky the"
Step 4: Return the Result
return reversed_string
- The reversed sentence is returned as the output.
Time and Space Complexity
- Time Complexity:
O(n)- We scan the entire string once to split, reverse, and join.
- Space Complexity:
O(n)- Temporary space for list of words and final string.
This solution The Reverse Words in a String uses Python’s built-in string and list functions to reverse the order of words in a string efficiently.
Conclusion
The Reverse Words in a String problem from LeetCode 75 is a powerful exercise in mastering string manipulation in Python. By focusing on trimming spaces, splitting words correctly, and reversing their order, you gain hands-on experience with core string operation. This problem not only tests your ability to clean and format input but also sharpens your understanding of Python’s built-in methods like .split() and .join(). Mastering this challenge sets a solid foundation for more advanced text-processing problems you’ll encounter in coding interviews and real-world applications.