Understanding the Problem

A string is given with spaces. The string could be a single character or a complete sentence. It is to reverse the string by words. The spaces at the edges should be cut off.

# example 1
Input: s = "the sky is blue"
Output: "blue is sky the"

# example 2
Input: s = "  the sky is blue  "
Output: "blue is sky the"

Approach

I would first make it a list, the reverse it. Quite a simple problem it seems.

Solution

I made the string a list by split() so it will automatically remove all the spaces and make a word list. s_list below will have the value s_list = [“the”, ”sky”, ”is”, ”blue”]. Afterwards, I reversed the list with s_list[::-1]. This index sorting means it will be reversed with the value -1. In slicing index has got the sequence as [start:stop:step]. When the step has a negative value, this means in a reverse order, so in our case it was to select every elements by emptying start and stop, then reverse it with -1 to enumerate every element.

When the list is reversed, then I simply joined the list.

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

Reflection

If I had no knowledge about the internal methods like split(), join() and slicing technique, this problem would’ve been a conundrum. Luckily my answer had the time complexity of 0ms.