Strings coding problems

String problems test careful indexing and clean parsing: palindromes, anagrams, counting characters, splitting and rebuilding text. They show up in service-company tests and product-company interviews alike.

35 problems: 18 easy, 15 medium, 2 hard. Free to read; a free account solves them and earns XP and Aura.

1. Check if Binary Representation is PalindromePractice · +10 XP · bit manipulation, stringseasy
2. Count Character OccurrencesPractice · +10 XP · strings, loops, countingeasy
3. Count Digit SumPractice · +10 XP · strings, loops, parsingeasy
4. Count Non-Alphabetic CharactersPractice · +10 XP · strings, counting, loopseasy
5. Count Specific CharactersPractice · +10 XP · strings, counting, loopseasy
6. Count Uppercase LettersPractice · +10 XP · strings, loops, countingeasy
7. Count Vowel OccurrencesPractice · +10 XP · dynamic programming, strings, iterationeasy
8. Count Vowel PairsPractice · +10 XP · strings, loops, countingeasy
9. First Occurrence of CharacterPractice · +10 XP · strings, string scanning, loopseasy
10. First Unique CharacterPractice · +10 XP · queue, string, frequency mapeasy
11. Most Frequent CharacterPractice · +10 XP · hash map, strings, countingeasy
12. Reverse a StringPractice · +10 XP · stack, stringeasy
13. Reverse WordsPractice · +10 XP · strings, loops, simple parsingeasy
14. Sort by Length and LexicographicallyPractice · +10 XP · sorting, stringseasy
15. String AnalyzerPractice · +10 XP · strings, counting, simple parsingeasy
16. String Symmetry CheckPractice · +10 XP · strings, loops, conditionalseasy
17. The Polite WaiterDaily · +5 XP · +3 Aura (late, half) · strings, counting, loops1 solvedeasy
18. Valid BracketsPractice · +10 XP · stack, stringseasy
19. Balanced Parentheses CheckPractice · +20 XP · recursion, strings, parsingmedium
20. Distinct Substring CountsPractice · +20 XP · strings, suffix automaton, data structuresmedium
21. Longest Alternating SubstringPractice · +20 XP · strings, sliding windowmedium
22. Longest Common SuffixPractice · +20 XP · strings, hashing, suffix arraymedium
23. Longest Palindromic SubsequencePractice · +20 XP · dynamic programming, string, lpsmedium
24. Longest Prefix With No RepeatsPractice · +20 XP · strings, sliding window, hash setmedium
25. Longest Repeating SubstringPractice · +20 XP · strings, suffix array, lcp arraymedium
26. Longest Substring With At Most K Distinct CharactersPractice · +20 XP · strings, sliding window, hash mapmedium
27. Longest Substring Without RepeatsPractice · +20 XP · sliding window, hash map, stringsmedium
28. Longest Symmetric SubstringPractice · +20 XP · strings, dynamic programming, two pointersmedium
29. Most Frequent SubstringPractice · +20 XP · strings, hashing, countingmedium
30. String BalancePractice · +20 XP · strings, two pointersmedium
31. String PartitionPractice · +20 XP · strings, hashing, prefix sumsmedium
32. String with Most Unique CharactersPractice · +20 XP · strings, sliding window, hash mapmedium
33. Substring ParityPractice · +20 XP · strings, prefix sums, paritymedium
34. Distinct Subsequences CountPractice · +30 XP · hash map, dynamic programming, stringhard
35. Minimum Window SubstringPractice · +30 XP · sliding window, two pointers, stringshard