ProgramsJava

Module 4: String Programs

reverse, palindrome, split, regex. Strings are where beginners leak hours. equals(), not ==.

25 programs · open one, then the next

Start with Reverse String
  1. 01Reverse StringBeginnerReverse a given string using a loop.Open example →
  2. 02Check Palindrome StringBeginnerCheck whether a string is a palindrome.Open example →
  3. 03Count VowelsBeginnerCount the number of vowels in a string.Open example →
  4. 04Count ConsonantsBeginnerCount the number of consonants in a string.Open example →
  5. 05Count WordsBeginnerCount the number of words in a sentence.Open example →
  6. 06Remove WhitespaceBeginnerRemove all whitespace characters from a string.Open example →
  7. 07Remove Duplicate CharactersIntermediateRemove duplicate characters from a string, keeping first occurrences.Open example →
  8. 08Anagram CheckIntermediateCheck whether two strings are anagrams of each other.Open example →
  9. 09String RotationIntermediateCheck if one string is rotation of another.Open example →
  10. 10Frequency of CharactersIntermediateCount frequency of each character in a string.Open example →
  11. 11Longest WordBeginnerFind the longest word in a sentence.Open example →
  12. 12Shortest WordBeginnerFind the shortest word in a sentence.Open example →
  13. 13Replace SubstringBeginnerReplace all occurrences of a substring in a string.Open example →
  14. 14Reverse Words in SentenceBeginnerReverse the order of words in a sentence.Open example →
  15. 15Sort CharactersBeginnerSort characters of a string in ascending order.Open example →
  16. 16Convert to Title CaseBeginnerConvert a sentence to title case (first letter of each word uppercase).Open example →
  17. 17Count Uppercase LettersBeginnerCount number of uppercase letters in a string.Open example →
  18. 18Count Lowercase LettersBeginnerCount number of lowercase letters in a string.Open example →
  19. 19Extract NumbersBeginnerExtract all numbers (digits) from a string.Open example →
  20. 20Validate Email (Regex)IntermediateValidate email format using a simple regex.Open example →
  21. 21Validate PasswordIntermediateCheck if a password meets basic strength rules using regex.Open example →
  22. 22Check PangramIntermediateCheck whether a sentence is a pangram (contains all letters A–Z).Open example →
  23. 23Split & Join StringsBeginnerSplit a sentence into words and then join them with a different delimiter.Open example →
  24. 24String CompressionIntermediateCompress a string as character followed by count (basic run-length encoding).Open example →
  25. 25String PermutationsAdvancedGenerate all permutations of a string using recursion.Open example →