String Data Structures and Algorithms: Essential Interview Questions.

Mastering string-related data structures and algorithms is crucial for coding interviews, as they test problem-solving abilities and understanding of string manipulation techniques. Here’s a categorized list of common string problems, including basic operations, algorithms, and advanced manipulations that are commonly asked in interviews.

1. Basic String Operations

• Reverse a String: Reverse the characters of a string in place.
• Check if a String is a Palindrome: Verify if a string reads the same forward and backward.
• Count Vowels and Consonants in a String: Calculate the number of vowels and consonants.
• Check if Two Strings are Anagrams: Determine if two strings contain the same characters in different orders.
• Remove All Occurrences of a Character: Eliminate a specified character from a string.
• Find the First Non-Repeating Character: Identify the first character that does not repeat in the string.
• Find the Last Non-Repeating Character: Locate the last character in the string that appears only once.
• Convert a String to Uppercase/Lowercase: Change the case of all characters.
• Remove Whitespace: Strip out all spaces and tabs from the string.
• Count the Frequency of Each Character: Create a frequency map of characters.

2. String Matching and Searching

• Implement Naive String-Matching Algorithm: Basic pattern-matching technique.
• Knuth-Morris-Pratt (KMP) Algorithm: Efficiently find patterns using prefix tables.
• Rabin-Karp Algorithm: Uses hashing for substring search.
• Boyer-Moore Algorithm: Skips sections of text for faster pattern matching.
• Find All Occurrences of a Pattern in a Text (Using KMP).
• Find All Anagrams of a Pattern in a Text (Sliding Window): Locate all anagrams using a window of fixed size.
• Find the Longest Prefix Suffix (LPS) Array: Preprocess for KMP.
• Find the First Occurrence of a Substring.
• Check if a String Contains Another String: Perform substring search.
• Count the Number of Occurrences of a Pattern.

3. String Manipulation

• Rotate a String by N Characters: Shift characters to the left or right.
• Swap Two Characters in a String.
• Remove Duplicates from a String: Ensure each character appears only once.
• Replace All Occurrences of a Substring: Substitute a given substring with another.
• Merge Two Strings Alternately.
• Find the Longest Common Substring.
• Find the Longest Common Prefix.
• Find the Longest Repeating Substring.
• Reverse Words in a String: Reverse the order of words.
• Remove All Adjacent Duplicates.

4. String Transformations

• Convert a String to an Integer/Float: Parse strings into numerical values.
• Implement String Compression/Decompression.
• Find the Minimum Window Substring Containing All Characters.
• Find the Maximum Repeating Character.
• Count Distinct Substrings in a String.
• Implement a Simple Text Formatter.
• Convert to Title Case/Camel Case.

5. String Algorithms

• Implement a Trie: For efficient prefix-based searching.
• Find the Longest Palindromic Substring: Use dynamic programming or expand around center technique.
• Longest Common Subsequence (LCS).
• Shortest Common Supersequence.
• Minimum Insertions/Deletions for a Palindromic String.
• Edit Distance (Levenshtein Distance).
• Suffix Array/Tree Implementation.
• Longest Increasing Subsequence in a String.

6. String Comparison

• Compare Strings (Ignoring/Respecting Case).
• Check if One String is a Rotated Version of Another.
• Check if a String is a Subsequence.
• Check if a String Contains Unique Characters.
• Validate String as a Parentheses Sequence.

7. String Patterns and Regular Expressions

• Implement Regular Expression Matching.
• Find Substrings Using Regular Expressions.
• Validate Email, Phone Number, and URL.
• Extract Dates/Phone Numbers from a String.
• Replace Words Using Regex.

8. String Rotations and Shifts

• Check if One String is a Rotation of Another.
• Rotate a String (Left/Right).
• Find the Minimum/Maximum Rotations to Match.
• Implement a Circular Buffer.
• Shift Characters by N Positions.

9. Advanced String Manipulations

• Encode and Decode Strings.
• Implement a Basic Text Editor.
• Find All Permutations/Combinations of a String.
• Find the Smallest Window Substring.
• Calculate Longest Common Prefix Length.

By understanding and practicing these problems, you'll be well-equipped to handle string-related challenges in coding interviews. Each category is designed to build skills progressively, ensuring a well-rounded mastery of string manipulation and pattern recognition. Happy coding!

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