#Strings

Valid Parentheses

Group Anagrams

Longest Substring Without Repeating Characters

Remove Duplicate Characters from a String

Check if a String Contains Only Digits

Reverse Words in a Sentence

First Non-Repeating Character in a String

Count Frequency of Characters in a String

Check if Two Strings Are Anagrams

Check if a String Is a Palindrome

Reverse a String In Place

StringBuilder and StringBuffer in Java

When text is built piece by piece, a mutable buffer avoids the copying that repeated String concatenation forces.