Strings

Parsing, palindromes, anagrams and text processing.

107 problems

Title	Tags	Acceptance	Difficulty
1. Longest Common Subsequence	Dynamic Programming · String	—	Medium
2. Edit Distance	Dynamic Programming · String	—	Hard
3. Valid Parentheses	Stack · String	—	Easy
4. Palindrome Check	String · Two Pointers	—	Easy
5. Valid Anagram	String · Hash Map · Sorting	—	Easy
6. Reverse Words	String	—	Easy
7. String Compression	String · Run-Length Encoding	—	Easy
8. Caesar Cipher	String · Math	—	Easy
9. First Unique Character	String · Hash Map	—	Easy
10. Longest Palindromic Substring	String · Expand Around Center	—	Medium
11. Count Vowels and Consonants	String	—	Easy
12. Word Frequency	String · Hash Map · Sorting	—	Easy
13. snake_case to camelCase	String	—	Easy
14. Reverse a String	String	—	Easy
15. Count Letters, Digits and Spaces	String	—	Easy
16. Toggle Case	String	—	Easy
17. Count Words	String · Parsing	—	Easy
18. Capitalise Each Word	String	—	Easy
19. Remove Vowels	String	—	Easy
20. Character Frequency	Hash Map	—	Easy
21. Isogram Check	Set	—	Easy
22. Pangram Check	Set	—	Easy
23. Longest Word	String	—	Easy
24. Is It a Rotation?	String	—	Easy
25. Run-Length Decoding	String · Parsing	—	Easy
26. First Non-Repeating Character Index	Hash Map	—	Easy
27. Longest Common Prefix	String	—	Easy
28. Valid Palindrome (Letters and Digits)	Two Pointers	—	Easy
29. Longest Substring Without Repeats	Sliding Window	—	Medium
30. Count Anagram Groups	Hash Map · Sorting	—	Medium
31. Split into Balanced Strings	Greedy · Counting	—	Easy
32. String to Integer	Parsing	—	Medium
33. Roman to Integer	Hash Map	—	Easy
34. Integer to Roman	Greedy	—	Medium
35. Count Palindromic Substrings	Expand Around Centre	—	Medium
36. Most Frequent Character	Counting	—	Easy
37. Is Subsequence	Two Pointers	—	Easy
38. Reverse Only the Vowels	Two Pointers	—	Easy
39. Word Pattern	Hash Map · Bijection	—	Easy
40. Isomorphic Strings	Hash Map	—	Easy
41. Make Anagrams	Counting	—	Easy
42. Caesar Decoder	String · Modular Arithmetic	—	Easy
43. Longest Run After K Changes	Sliding Window	—	Medium
44. Minimum Window Containing All	Sliding Window	—	Hard
45. Decode Ways	Dynamic Programming	—	Medium
46. One Edit Away	Two Pointers	—	Medium
47. Zigzag Conversion	Simulation	—	Medium
48. Repeated Substring Pattern	String	—	Easy
49. Count and Say	Simulation	—	Medium
50. Valid Interleaving	Dynamic Programming	—	Hard
51. Count Binary Substrings	Counting	—	Easy
52. Excel Column Title	Number Bases	—	Easy
53. Excel Column Number	Number Bases	—	Easy
54. Sort Words by Length	Custom Sort	—	Easy
55. Top K Frequent Words	Hash Map · Sorting	—	Medium
56. Decode String	Stack · Parsing	—	Medium
57. Simplify Unix Path	Stack	—	Medium
58. Phone Keypad Combinations	Backtracking	—	Medium
59. Palindrome Partitions	Backtracking	—	Medium
60. Longest Common Substring	Dynamic Programming	—	Medium
61. Longest Palindromic Subsequence	Dynamic Programming	—	Medium
62. Minimum Insertions for Palindrome	Dynamic Programming	—	Medium
63. Word Break	Dynamic Programming	—	Medium
64. Distinct Subsequence Count	Dynamic Programming · Counting	—	Hard
65. Wildcard Matching	Dynamic Programming	—	Hard
66. Regular Expression Matching	Dynamic Programming	—	Hard
67. Largest Number	Custom Sort	—	Medium
68. Word Ladder	BFS	—	Hard
69. 12-Hour to 24-Hour Time	Parsing	—	Easy
70. Password Strength	Validation	—	Easy
71. Validate an IPv4 Address	Parsing · Validation	—	Medium
72. Validate an Email Address	Validation	—	Medium
73. Word Wrap	Greedy	—	Medium
74. Centre the Text	Formatting	—	Easy
75. Number to Words	Recursion · Formatting	—	Hard
76. Palindrome After One Deletion	Two Pointers	—	Easy
77. Backspace String Compare	Stack · Two Pointers	—	Easy
78. Longest Substring With K Distinct Characters	Sliding Window	—	Medium
79. Permutation in String	Sliding Window	—	Medium
80. Find All Anagrams in a String	Sliding Window	—	Medium
81. Maximum Vowels in a Substring of Length K	Sliding Window	—	Medium
82. Partition Labels	Greedy	—	Medium
83. Ransom Note	Counting	—	Easy
84. Jewels and Stones	Hash Set	—	Easy
85. Uncommon Words From Two Sentences	Hash Map	—	Easy
86. Custom Sort String	Sorting	—	Medium
87. Longest Palindrome You Can Build	Counting	—	Easy
88. Determine if Two Strings Are Close	Counting	—	Medium
89. Maximum Number of Balloons	Counting	—	Easy
90. Bulls and Cows	Counting	—	Medium
91. Find the Difference	Bit Manipulation · Counting	—	Easy
92. Add Binary	Math	—	Easy
93. Add Strings	Math	—	Easy
94. Multiply Strings	Math	—	Medium
95. Compare Version Numbers	Parsing	—	Medium
96. Length of Last Word	String	—	Easy
97. License Key Formatting	String	—	Easy
98. Detect Capital	String	—	Easy
99. Student Attendance Record	String	—	Easy
100. Robot Return to Origin	Simulation	—	Easy
101. Shortest Distance to a Character	Two Pass	—	Easy
102. Reverse Each Word	String	—	Easy
103. Reverse String II	String	—	Easy
104. Defang an IP Address	String	—	Easy
105. Final Value After Operations	Simulation	—	Easy
106. Goal Parser Interpretation	String	—	Easy
107. Count Consistent Strings	Hash Set	—	Easy

107 of 107 problems