24-string-exercise.md

String Exercise

Easy:

1. Write a program to reverse a string.
2. Check if a given string is a palindrome.
3. Count the number of vowels in a string.
4. Convert a string to uppercase.
5. Convert a string to lowercase.
6. Find the length of a string without using the built-in length property.
7. Remove all spaces from a string.
8. Concatenate two strings without using the + operator.
9. Find the first non-repeated character in a string.
10. Replace all occurrences of a substring with another substring in a given string.
11. Remove all occurrences of a specified character from a string.
12. Check if a string starts with a specific substring.
13. Check if a string ends with a specific substring.
14. Count the number of words in a sentence.
15. Remove duplicate characters from a string.
16. Convert a sentence to title case (capitalize the first letter of each word).
17. Swap the case of each character in a string (e.g., 'Hello' becomes 'hELLO').
18. Find the most frequent character in a string.
19. Implement a function to truncate a string if it's longer than a certain length, adding "..." at the end.
20. Check if a string is a valid URL.

Medium:

1. Implement a function to check if two strings are anagrams.
2. Check if a string contains only digits.
3. Count the occurrences of a specific word in a paragraph.
4. Reverse the order of words in a sentence.
5. Capitalize the first letter of each word in a sentence.
6. Find the longest substring without repeating characters.
7. Rotate a string to the left by a given number of positions.
8. Check if a string is a valid email address.
9. Implement a function to perform string compression (e.g., "aabcccccaaa" becomes "a2b1c5a3").
10. Calculate the Levenshtein distance between two strings.
11. Implement a function to convert a string to camel case.
12. Check if a string is a valid IPv4 address.
13. Reverse the order of words and the characters within each word in a sentence.
14. Write a program to remove all HTML tags from a string.
15. Implement a function to encode a string using Run-Length Encoding (e.g., "aaabbbbbcc" becomes "a3b5c2").
16. Find the longest common prefix of an array of strings.
17. Implement a function to decode a Run-Length Encoded string.
18. Implement a function to perform base64 encoding and decoding.
19. Check if a string contains a valid date in a specific format (e.g., "MM/DD/YYYY").
20. Implement a function to convert a string to "snake_case".

Tough:

1. Implement the indexOf function without using the built-in method.
2. Find the longest palindrome substring in a given string.
3. Implement regular expression matching for a simple pattern (e.g., ".ab" matches "aaaab").
4. Write a program to reverse words in a sentence while preserving whitespace.
5. Implement a function to perform basic string parsing similar to a compiler's lexer.
6. Count the number of distinct substrings in a string.
7. Implement the split function without using the built-in method.
8. Write a program to generate all possible permutations of a string.
9. Implement a function to calculate the edit distance between two strings.
10. Find the shortest superstring that contains all given strings as substrings.
11. Implement a function to reverse words in a sentence, while keeping the words' relative order unchanged (e.g., "The quick brown fox" becomes "ehT kciuq nworb xof").
12. Implement a function to find the longest substring with at most K distinct characters.
13. Write a program to format a multi-line text into a paragraph (word wrapping).
14. Check if a given string follows a specific pattern (e.g., "abab" matches "redblueredblue").
15. Implement a function to find the shortest palindrome that can be formed by adding characters to the end of a given string.
16. Count the number of anagrams of a given word in a list of words.
17. Implement a function to find the minimum window in a string that contains all characters of another string.
18. Check if a string is a valid Roman numeral.
19. Write a program to generate all valid IP addresses from a given string containing digits.
20. Implement a function to reverse the order of words in a sentence, while preserving the spaces and punctuation.