151. Reverse Words in a String

Tags: #twopointers #string #medium

Problem Statement

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.

Input: s = "  hello world  "
Output: "world hello"
Explanation: Your reversed string should not contain leading or trailing spaces.

My approach

class Solution:
    def reverseWords(self, s: str) -> str:
        a = s.split()
        if ( len(a) == 1):
            return s
        return " ".join(a[::-1])

In my approach, I kinda cheated for this problem since I used python's built in methods to first split the given string into an array of words using s.split() and then checked if the length of the array was 1, if it was returned the original string otherwise I first reversed the array through a[::-1] and then used " ".join() to add the spaces in between words and return a string.

class Solution:
    def reverseWords(self, s: str) -> str:
        i = 0
        j = len(s)-1
        # Remove Front Spaces
        while i < len(s) and s[i] == " ":
            i += 1
        # Remove back spaces
        while j >= 0 and s[j] == " ":
            j -= 1
        ans = []
        # run while we dont get to initial valid index i
        while j >= i:
            # Trim middle spaces
            while j >= i and s[j] == " ":
                j -= 1
            # Make  word reverse it 
            temp = []
            while j >= i and s[j] != " ":
                temp.append(s[j])
                j -= 1
            # Append word to original ans
            ans.append("".join(temp[::-1]))
        return " ".join(ans)

Although my approach isn't the modal solution for the problem, I have found this solution which matches the LeetCode Description and solves the problem statement using the two pointer approach. The code comments pretty much explain the code.

Personal Thoughts

Well even though I took the more hacky approach, I do think it is a valid solution to the problem since there were no restrictions in the problem statement (Foreshadowing). I learned a lot too by going through the other solution that's why I included it here.