June 20th 2023

Reverse Words in a String — Typescript

Problem 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.

Solution

function expect(description: string, test: boolean) {
    if (test) {
        console.log(`✅ ${description}`)
    } else {
        console.log(`❌ ${description}`)
    }
}


function reverseWords(s: string): string {
    return s
        .trim()
        .split(/\s+/g)
        .reverse()
        .join(" ")
}


expect("Simple example", reverseWords("the sky is blue") == "blue is sky the")
expect("Leading and trailing space", reverseWords("  hello world  ") == "world hello")
expect("complex spacing", reverseWords("a good   example") == "example good a")

Discussion

This problem was a quick warmup stretch. It helps that my life is regular expressions right now so it was immediately obvious that this was going to need a regex to split on space. Really this function does two things- it's doing a string sanitization on an input (removing leading and trailing space, breaking up into tokens based on a space delimeter) AND THEN it's doing a reversal. If this was something to be shipped in production I would be very tempted to break up those responsibilities into several functions so that they could be tested (maybe sanitize, tokenize, reverseWords). For this little stretch, though, it's ok for all of those concerns to live together in a single function.