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AlgorithmBeginner
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String Manipulation

Transform and analyze text

⏱️ 6–10 hours🧩 10 LeetCode
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What is it?

A string is just text — a sequence of characters. String manipulation is what you do when you want to transform, inspect, or extract parts of that text.

Think of it like editing a word document: lower-case everything, find a word, swap it for another, or read it backwards.

Common Techniques

  • Two pointers — check palindromes or reverse in-place
  • Frequency map — detect anagrams, count characters
  • Stack — validate bracket pairs, decode compressed strings
  • Sliding window — find the longest substring without repeats
  • HashMap — group anagrams together

Real-World Examples

Password strength check
Autocorrect & spellcheck
CSV / JSON text parsing
URL slug generator
Find & Replace in editor
Plagiarism detection

Code Example

What this code shows

On 'Hello, World!': lower-case converts every letter to its small form. includes() checks whether the substring 'World' exists inside. Reversing the characters gives the string read backwards.

const s = "Hello, World!";

// convert every character to lower-case
console.log(s.toLowerCase()); // "hello, world!"

// check if a substring exists anywhere inside
console.log(s.includes("World")); // true

// spread into chars, reverse the array, join back to string
console.log([...s].reverse().join("")); // "!dlroW ,olleH"

Expected Output

hello, world!
true
!dlroW ,olleH

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