Reverse Words in a Sentence

Reversing Word Order

Reversing words in a sentence means rearranging the words so the last word comes first, while keeping the characters within each word unchanged.

Example

Input:  "The quick brown fox jumps"
Output: "jumps fox brown quick The"

Each word retains its original spelling — only the order changes.

Algorithm

Split-reverse-join approach:

const result = sentence.split(/\s+/).reverse().join(" ");

In-place approach (O(1) extra space):

1. Reverse the entire string character by character
2. Reverse each individual word within the result

Step 0: "The quick brown fox"
Step 1: "xof nworb kciuq ehT"  (reverse all characters)
Step 2: "fox brown quick The"  (reverse each word)

This two-pass technique is a classic interview solution because it achieves word reversal without allocating a new array.

Edge Cases to Consider

• Multiple spaces: Should consecutive spaces be collapsed to one, or preserved?
• Leading/trailing spaces: Should they be trimmed or kept?
• Single word: Returns the same word unchanged
• Empty string: Returns empty string
• Newlines: Should each line be processed independently?

Multi-line Handling

When processing multi-line text, words are typically reversed within each line independently:

Input:
  "Hello World"
  "Good Morning"

Output:
  "World Hello"
  "Morning Good"

This preserves the line structure while reversing word order within each line.