Reverse Sentence - FreeCodeCamp #32 Daily Challenge

2025-12-22 1 min

Table of Contents

Reverse Sentence — Analysis & Explanation 🚀

Problem Statement

Given a string of words, return a new string with the words in reverse order. For example, the first word should be at the end and the last word at the beginning.

Conditions:

Words may be separated by one or more spaces.
The returned string must have only one space between each word.

Initial Analysis

What does the challenge ask?

Reverse the order of the words and normalize spaces. That is:

Correctly split the words (ignoring extra spaces).
Reorder and print them in reverse order, separated by a single space.

For this, JavaScript’s split, reverse, and join methods are ideal.

Key Test Cases

Input: "world hello" → Output: "hello world"
Input: "push commit git" → Output: "git commit push"
Input: "npm install sudo" → Output: "sudo install npm"
Input: "import default function export" → Output: "export function default import"

All cases normalize spaces and reverse the word order.

Solution Development

Strategy

Split using .split(/\s+/) to get only words.
Reverse the array.
Join with .join(' ') to ensure a single space.

JavaScript Implementation

function reverseSentence(sentence) {
  return sentence
    .trim() // Remove leading/trailing spaces
    .split(/\s+/) // Split into words, ignore extra spaces
    .reverse() // Reverse the array
    .join(' ') // Join with a single space
}

Complexity Analysis

Time

Each operation (trim, split, reverse, join) traverses the string or array once: $O(n)$

Space

Auxiliary arrays proportional to the input size are created: $O(n)$

Edge Cases & Considerations

Empty string or only spaces: returns "" (empty).
Leading/trailing spaces: are removed.
Multiple spaces between words: normalized to one.
Single word: returns the same, no extra spaces.

Reflections & Learnings

🔹 Strings & arrays: efficient manipulation in JS. 🔹 Regular expressions: robust against “messy” input. 🔹 Functional composition: readable and compact code.

💡 The solution is optimal and readable. No further optimizations needed.

Resources & References

freecodecamp daily-challenge