String
181 problems
String problems range from simple character counting to complex pattern matching. Common approaches include two pointers, sliding window, prefix hashing, and the KMP algorithm. In C#, strings are immutable — use StringBuilder for efficient concatenation inside loops.
- 12.Integer to RomanMedium
- 13.Roman to IntegerEasy
- 14.Longest Common PrefixEasy
- 22.Generate ParenthesesMedium
- 30.Substring with Concatenation of All WordsHard
- 32.Longest Valid ParenthesesHard
- 38.Count and SayMedium
- 44.Wildcard MatchingHard
- 58.Length of Last WordEasy
- 67.Add BinaryEasy
- 68.Text JustificationHard
- 76.Minimum Window SubstringHard
- 87.Scramble StringHard
- 126.Word Ladder IIHard
- 165.Compare Version NumbersMedium
- 166.Fraction to Recurring DecimalMedium
- 171.Excel Sheet Column NumberEasy
- 179.Largest NumberMedium
- 212.Word Search IIHard
- 214.Shortest PalindromeHard
- 241.Different Ways to Add ParenthesesMedium
- 257.Binary Tree PathsEasy
- 273.Integer to English WordsHard
- 299.Bulls and CowsUnknown
- 316.Remove Duplicate LettersMedium
- 331.Verify Preorder Serialization of a Binary TreeUnknown
- 344.Reverse StringEasy
- 467.Unique Substrings in Wraparound StringMedium
- 474.Ones and ZeroesMedium
- 500.Keyboard RowEasy
- 539.Minimum Time DifferenceMedium
- 564.Find the Closest PalindromeHard
- 567.Permutation in StringMedium
- 592.Fraction Addition and SubtractionUnknown
- 657.Robot Return to OriginUnknown
- 664.Strange PrinterHard
- 678.Valid Parenthesis StringMedium
- 696.Count Binary SubstringsEasy
- 709.To Lower CaseEasy
- 712.Minimum ASCII Delete Sum for Two StringsMedium
- 726.Number of AtomsHard
- 761.Special Binary StringUnknown
- 763.Partition LabelsMedium
- 784.Letter Case PermutationMedium
- 796.Rotate StringEasy
- 820.Short Encoding of WordsMedium
- 821.Shortest Distance to a CharacterEasy
- 838.Push DominoesMedium
- 839.Similar String GroupsHard
- 856.Score of ParenthesesMedium
- 880.Decoded String at IndexMedium
- 884.Uncommon Words from Two SentencesEasy
- 890.Find and Replace PatternMedium
- 902.Numbers At Most N Given Digit SetHard
- 916.Word SubsetsMedium
- 917.Reverse Only LettersEasy
- 921.Minimum Add to Make Parentheses ValidMedium
- 944.Delete Columns to Make SortedEasy
- 955.Delete Columns to Make Sorted IIMedium
- 960.Delete Columns to Make Sorted IIIHard
- 966.Vowel SpellcheckerMedium
- 981.Time Based Key-Value StoreMedium
- 1028.Recover a Tree From Preorder TraversalHard
- 1061.Lexicographically Smallest Equivalent StringMedium
- 1079.Letter Tile PossibilitiesMedium
- 1081.Smallest Subsequence of Distinct CharactersMedium
- 1092.Shortest Common SupersequenceHard
- 1106.Parsing A Boolean ExpressionHard
- 1190.Reverse Substrings Between Each Pair of ParenthesesMedium
- 1233.Remove Sub-Folders from the FilesystemMedium
- 1358.Number of Substrings Containing All Three CharactersMedium
- 1371.Find the Longest Substring Containing Vowels in Even CountsMedium
- 1392.Longest Happy PrefixUnknown
- 1400.Construct K Palindrome StringsUnknown
- 1405.Longest Happy StringUnknown
- 1408.String Matching in an ArrayUnknown
- 1410.HTML Entity ParserUnknown
- 1415.The k-th Lexicographical String of All Happy Strings of Length nUnknown
- 1422.Maximum Score After Splitting a StringUnknown
- 1455.Check If a Word Occurs As a Prefix of Any Word in a SentenceUnknown
- 1461.Check If a String Contains All Binary Codes of Size KMedium
- 1487.Making File Names UniqueUnknown
- 1513.Number of Substrings With Only 1sUnknown
- 1529.Minimum Suffix FlipsUnknown
- 1545.Find Kth Bit in Nth Binary StringEasy
- 1573.Number of Ways to Split a StringUnknown
- 1578.Minimum Time to Make Rope ColorfulMedium
- 1593.Split a String Into the Max Number of Unique SubstringsMedium
- 1598.Crawler Log FolderEasy
- 1625.Lexicographically Smallest String After Applying OperationsUnknown
- 1639.Number of Ways to Form a Target String Given a DictionaryHard
- 1653.Minimum Deletions to Make String BalancedMedium
- 1678.Goal Parser InterpretationUnknown
- 1684.Count the Number of Consistent StringsEasy
- 1689.Partitioning Into Minimum Number Of Deci-Binary NumbersMedium
- 1717.Maximum Score From Removing SubstringsUnknown
- 1758.Minimum Changes To Make Alternating Binary StringUnknown
- 1763.Longest Nice SubstringEasy
- 1768.Merge Strings AlternatelyEasy
- 1769.Minimum Number of Operations to Move All Balls to Each BoxMedium
- 1784.Check if Binary String Has at Most One Segment of OnesUnknown
- 1790.Check if One String Swap Can Make Strings EqualEasy
- 1813.Sentence Similarity IIIUnknown
- 1844.Replace All Digits with CharactersEasy
- 1859.Sorting the SentenceUnknown
- 1888.Minimum Number of Flips to Make the Binary String AlternatingUnknown
- 1910.Remove All Occurrences of a SubstringUnknown
- 1930.Unique Length-3 Palindromic SubsequencesMedium
- 1935.Maximum Number of Words You Can TypeUnknown
- 1945.Sum of Digits of String After ConvertUnknown
- 1948.Delete Duplicate Folders in SystemUnknown
- 1957.Delete Characters to Make Fancy StringUnknown
- 1963.Minimum Number of Swaps to Make the String BalancedUnknown
- 1967.Number of Strings That Appear as Substrings in WordUnknown
- 1980.Find Unique Binary StringMedium
- 2011.Final Value of Variable After Performing OperationsUnknown
- 2014.Longest Subsequence Repeated k TimesUnknown
- 2053.Kth Distinct String in an ArrayUnknown
- 2096.Step-By-Step Directions From a Binary Tree Node to AnotherMedium
- 2109.Adding Spaces to a StringEasy
- 2116.Check if a Parentheses String Can Be ValidMedium
- 2131.Longest Palindrome by Concatenating Two Letter WordsMedium
- 2138.Divide a String Into Groups of Size kUnknown
- 2182.Construct String With Repeat LimitMedium
- 2185.Counting Words With a Given PrefixEasy
- 2264.Largest 3-Same-Digit Number in StringEasy
- 2273.Find Resultant Array After Removing AnagramsUnknown
- 2337.Move Pieces to Obtain a StringMedium
- 2375.Construct Smallest Number From DI StringMedium
- 2379.Minimum Recolors to Get K Consecutive Black BlocksEasy
- 2416.Sum of Prefix Scores of StringsHard
- 2418.Sort the PeopleEasy
- 2434.Using a Robot to Print the Lexicographically Smallest StringMedium
- 2490.Circular SentenceEasy
- 2516.Take K of Each Character From Left and RightMedium
- 2559.Count Vowel Strings in RangesMedium
- 2573.Find the String with LCPUnknown
- 2609.Find the Longest Balanced Substring of a Binary StringEasy
- 2645.Minimum Additions to Make Valid StringMedium
- 2678.Number of Senior CitizensEasy
- 2696.Minimum String Length After Removing SubstringsEasy
- 2707.Extra Characters in a StringMedium
- 2785.Sort Vowels in a StringMedium
- 2825.Make String a Subsequence Using Cyclic IncrementsMedium
- 2839.Check if Strings Can be Made Equal With Operations IEasy
- 2840.Check if Strings Can be Made Equal With Operations IIMedium
- 2900.Longest Unequal Adjacent Groups Subsequence IEasy
- 2901.Longest Unequal Adjacent Groups Subsequence IIUnknown
- 2914.Minimum Number of Changes to Make Binary String BeautifulEasy
- 2930.Number of Strings Which Can Be Rearranged to Contain SubstringMedium
- 2942.Find Words Containing CharacterEasy
- 2976.Minimum Cost to Convert String IMedium
- 2977.Minimum Cost to Convert String IIUnknown
- 2981.Find Longest Special Substring That Occurs Thrice IMedium
- 2999.Count the Number of Powerful IntegersUnknown
- 3003.Maximize the Number of Partitions After OperationsUnknown
- 3016.Minimum Number of Pushes to Type Word IIMedium
- 3042.Count Prefix and Suffix Pairs IEasy
- 3043.Find the Length of the Longest Common PrefixEasy
- 3085.Minimum Deletions to Make String K-SpecialEasy
- 3136.Valid WordEasy
- 3163.String Compression IIIUnknown
- 3170.Lexicographically Minimum String After Removing StarsUnknown
- 3174.Clear DigitsEasy
- 3223.Minimum Length of String After OperationsUnknown
- 3227.Vowels Game in a StringUnknown
- 3234.Count the Number of Substrings With Dominant OnesEasy
- 3306.Count of Substrings Containing Every Vowel and K Consonants IIMedium
- 3330.Find the Original Typed String IEasy
- 3333.Find the Original Typed String IIUnknown
- 3335.Total Characters in String After Transformations IMedium
- 3337.Total Characters in String After Transformations IIUnknown
- 3403.Find the Lexicographically Largest String From the Box IUnknown
- 3442.Maximum Difference Between Even and Odd Frequency IMedium
- 3445.Maximum Difference Between Even and Odd Frequency IIMedium
- 3461.Check If Digits Are Equal in String After Operations IEasy
- 3474.Lexicographically Smallest Generated StringEasy
- 3541.Find Most Frequent Vowel and ConsonantUnknown
- 3606.Coupon Code ValidatorUnknown
- 3713.Longest Balanced Substring IUnknown
- 3714.Longest Balanced Substring IIUnknown