1. Implement a function to find the longest palindromic substring in a string.
2. Write a function to determine the minimum number of insertions required to make a string a palindrome.
3. Find the length of the longest substring without repeating characters.
4. Determine if a string can be rearranged to form a palindrome.
5. Implement a function to remove duplicate characters from a string without using extra space.
6. Reverse the words in a string while preserving the spaces.
7. Find all permutations of a given string.
8. Write a function to compress a string by replacing consecutive identical characters with the count of occurrences (e.g., "aaabb" becomes "a3b2").
9. Find the first non-repeating character in a string in constant time.
10. Implement a function to find the longest common subsequence of two strings.
11. Write a function to check if one string is a rotation of another string.
12. Determine if two strings are k-anagrams, where two strings are considered k-anagrams if they can be made identical with at most k changes.
13. Find the longest repeating substring in a string.
14. Implement a function to check if two strings are one edit distance apart.
15. Convert a given string into its zigzag pattern with a specified number of rows.
16. Write a function to find the longest palindromic subsequence in a string.
17. Implement a function to remove the adjacent duplicate characters in a string (e.g., "abbaca" becomes "ca").
18. Write a function to check if a string is a valid shuffle of two other strings.
19. Find all possible palindrome partitions of a string.
20. Implement a function to find the lexicographically smallest rotation of a string.
21. Write a function to decode a string encoded with run-length encoding (e.g., "a3b2" becomes "aaabb").
22. Determine the number of distinct subsequences of a given string.
23. Write a function to find all subsequences of a string that are palindromes.
24. Implement a function to perform a case-insensitive comparison of two strings.
25. Write a function to check if a given string can be rearranged into a word ladder.
26. Implement a function to find the length of the shortest transformation sequence from one string to another using a dictionary of words.
27. Write a function to find the length of the longest prefix which is also a suffix.
28. Implement a function to calculate the edit distance between two strings.
29. Write a function to generate all valid permutations of parentheses from a given string.
30. Find the minimum number of operations required to convert one string into another.
31. Implement a function to remove all characters from a string that appear in another string.
32. Write a function to determine if a string contains all the permutations of a shorter string.
33. Implement a function to split a string into all possible palindromic substrings.
34. Write a function to check if a string follows a given pattern (e.g., "abba" and "dog cat cat dog").
35. Implement a function to find the longest string chain in a dictionary of strings.
36. Write a function to find the minimum window in a string that contains all characters of another string.
37. Implement a function to count the number of distinct palindromic substrings in a string.
38. Write a function to generate all combinations of a string’s characters.
39. Implement a function to perform basic string compression using a modified version of run-length encoding.
40. Write a function to determine if a string can be divided into k parts with equal frequencies of each character.