Reverse String Basics

What Is String Reversal?

String reversal is one of the most fundamental operations in text processing and computer science. It takes a sequence of characters and produces a new sequence with the characters in the opposite order.

How It Works

Given the string "Hello, World!", character-by-character reversal produces:

Input:  H e l l o ,   W o r l d !
Output: ! d l r o W   , o l l e H

Every character — including spaces, punctuation, and special characters — is included in the reversal.

Common Algorithms

Two-pointer approach (in-place):

1. Place one pointer at the start, one at the end
2. Swap the characters at both pointers
3. Move pointers toward the center
4. Repeat until they meet

Stack-based approach:

1. Push each character onto a stack
2. Pop all characters off the stack
3. The LIFO order produces the reversed string

Built-in methods (JavaScript):

const reversed = [...str].reverse().join("");

Note that using str.split("").reverse().join("") can break with emoji and multi-byte Unicode characters. The spread operator [...str] correctly handles Unicode code points.

Time and Space Complexity

• Time complexity: O(n) — every character must be visited once
• Space complexity: O(n) — a new string of the same length is created

String reversal is a building block for many other algorithms, including palindrome detection, certain sorting algorithms, and text transformation pipelines.