Strings
Introduction to Strings
A string is a fundamental linear data structure that represents a sequence of characters. Unlike primitive data types such as integers or floats, strings handle textual information and can contain letters, numbers, spaces, symbols, and special characters. Strings are essentially character arrays with additional properties and built-in functionality that make text processing more convenient and powerful.
In most programming languages, strings are enclosed in double quotes (e.g., "Hello World"), though some languages also support single quotes.
String Representation and Memory Layout
Internal Structure
Strings are typically implemented as contiguous memory blocks containing character data. The exact representation varies by programming language and implementation:
Character Array Representation:
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Each character occupies one memory position
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Characters are indexed starting from 0
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Sequential storage enables efficient access
For accessing any character in a string: str[i] = Base Address + (i × sizeof(char))
Time Complexity
| Operation | Time Complexity | Explanation |
|---|---|---|
| Access by index | O(1) | Direct access using index is constant time. |
| Concatenation | O(n + m) | Combining two strings of lengths n and m requires copying both. |
| Substring extraction | O(k) | Extracting a substring of length k requires copying k characters. |
| Search for substring | O(n * m) | Naive search checks each position, leading to O(n*m) in worst case. |
| Comparison | O(n) | Comparing two strings of length n requires checking each character. |
| Insertion | O(n) | Inserting a character requires shifting elements, so linear time. |
| Deletion | O(n) | Deleting a character requires shifting elements, so linear time. |
Benefits of Strings
- Strings are easy to use and understand, making them a fundamental data type in programming.
- They provide a way to represent and manipulate text data effectively.
- Strings support various built-in functions and methods for common operations like searching, slicing, and formatting.
- They can be concatenated, split, and transformed using a variety of algorithms.
- Strings are immutable in many languages, which can lead to safer and more predictable code.
Limitations of Strings
- Strings can be memory-intensive, especially when dealing with large texts or frequent modifications.
- Insertion and deletion operations are costly
(O(n))due to the need to shift characters - Strings are immutable in many languages, meaning any modification creates a new string, which can lead to performance overhead.
- Handling multi-byte characters (like Unicode) can complicate string manipulation and indexing.
- Strings can lead to security vulnerabilities if not handled properly, such as buffer overflows or injection attacks.
When to Use Strings?
00
Text Representation
Use strings to represent and manipulate text data, such as names, messages, or documents.
01
Data Parsing
Ideal for parsing structured data formats like JSON, XML, or CSV.
02
Search and Pattern Matching
Useful for searching substrings or patterns within larger texts using algorithms like KMP or Rabin-Karp.
03
Input Handling
Commonly used for handling user input in applications, such as form data or command-line arguments.
04
Immutable Data
When you need immutable sequences of characters that should not change after creation.
05
String Manipulation
For tasks involving string manipulation, such as formatting, trimming, or case conversion.
How to Implement Strings in Different Languages
| Language | Mutability | Example Declaration |
|---|---|---|
| C | Mutable | char str[] = "hello"; |
| C++ | Mutable | std::string s = "hello"; |
| Java | Immutable | String s = "hello"; |
| Python | Immutable | s = "hello" |
| JS | Immutable | let s = "hello"; |
LeetCode Problems
| Problem Title | Difficulty | Short Description |
|---|---|---|
| Longest Substring Without Repeating Characters | Medium | Find the length of the longest substring with all unique characters. |
| Valid Anagram | Easy | Check if two strings are anagrams of each other. |
| Group Anagrams | Medium | Group strings that are anagrams together. |
| Valid Palindrome | Easy | Determine if a string is a palindrome after removing non-alphanumeric characters. |
| Palindromic Substrings | Medium | Count how many substrings in a string are palindromes. |
| Longest Palindromic Substring | Medium | Find the longest palindromic substring in a given string. |
| Minimum Window Substring | Hard | Find the minimum window substring that contains all characters of another string. |
| Regular Expression Matching | Hard | Implement regex matching with support for . and *. |
| Wildcard Matching | Hard | Match a string against a pattern with ? and *. |
| Implement strStr() | Easy | Return the index of the first occurrence of a substring. |
| Integer to Roman | Medium | Convert an integer to its Roman numeral representation. |
| Roman to Integer | Easy | Convert a Roman numeral to an integer. |
| Longest Common Prefix | Easy | Find the longest common prefix among an array of strings. |
| Edit Distance | Hard | Find the minimum operations to convert one string to another. |
| Word Break | Medium | Determine if a string can be segmented into dictionary words. |
| Word Break II | Hard | Return all possible segmentations of a string into dictionary words. |
| Decode Ways | Medium | Count the ways to decode a digit string into letters. |
| Substring with Concatenation of All Words | Hard | Find all starting indices where concatenation of words appears. |
| Find All Anagrams in a String | Medium | Find all indices of anagrams of a pattern in a string. |
| Repeated Substring Pattern | Easy | Check if a string is formed by repeating a substring pattern. |