String Problems

1. Reverse a string.
2. Check whether a string is a palindrome.
3. Count each character’s frequency.
4. Find the first non-repeating character.
5. Check whether two strings are anagrams.
6. Remove duplicate characters while preserving order.
7. Find the longest word in a sentence.
8. Compress repeated characters, such as aaabb to a3b2.
9. Check whether a string contains only digits without using isdigit().
10. Find the longest common prefix in a list of words.