📑 Table of Contents#

1. 📘 DSA: Strings Learning Roadmap (Beginner → Advanced) 1.1. 1. Basics of Strings (Foundations) 1.2. 🔍 2. Two Pointers on Strings 1.3. 🪟 3. Sliding Window (Very Important) 1.4. 🧮 4. Hashing for Strings 1.5. 🔤 5. Pattern Matching Algorithms 1.6. 6. Advanced String Topics
2. 📝 Must Do String Problems 2.1. 🔹 Level 1 – Easy 2.2. 🔹 Level 2 – Medium 2.3. 🔹 Level 3 – Hard

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🎯 Main Topics Covered#

1. 1 Basics of Strings Foundations
2. 2 Two Pointers on Strings
3. 3 Sliding Window Very Important
4. 4 Hashing for Strings
5. 5 Pattern Matching Algorithms
6. img src assetsiconspuzzlesvg relative_url classinline-icon alt 6 Advanced String Topics
7. Level 1 Easy
8. Level 2 Medium … and 1 more

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📘 DSA: Strings Learning Roadmap (Beginner → Advanced)#

1. Basics of Strings (Foundations)#

These are must-know before solving problems.

• Mutable vs Immutable (C++: std::string is mutable)

• Character arrays vs string class

• Common operations: length, substring, concatenation, comparison

• ASCII & Unicode basics

-> Click here for more details#

🔍 2. Two Pointers on Strings#

Used for many interview problems (palindrome, substring checks).

Key patterns:

• Move pointers from left & right

• Shrink/expand window on conditions

🪟 3. Sliding Window (Very Important)#

Strings + Sliding Window = 20% of interview questions.

Understand two types:#

🔸 Fixed Window#

E.g., find anagrams of a pattern.

🔸 Variable Window#

E.g., longest substring with K distinct characters.

🧮 4. Hashing for Strings#

Character frequency arrays#

• For lowercase → size 26

• For ASCII → size 256

• For Unicode → use hash maps

Rolling Hash / Rabin-Karp#

• Efficient substring search

• Used for detecting duplicate substrings, plagiarism, etc.

Interview problems:#

• Rabin-Karp implementation

• Longest duplicate substring (binary search + rolling hash)

🔤 5. Pattern Matching Algorithms#

KMP (Knuth–Morris–Pratt)#

Why important?

• Used for substring search in O(n + m)

• LPS array is commonly asked in interviews.

Z-Algorithm#

• Alternate fast pattern matching

• Helps in string prefix-based problems

Trie (String Tree)#

• Useful for autocomplete, prefix search, dictionary problems

Problems:#

• Word search

• Longest common prefix

• Implement Trie

6. Advanced String Topics#

These help in elite interviews.

Suffix Array#

• Used for lexicographical ordering of suffixes

• Applications: substring search, LCP computation

Suffix Tree / Compressed Trie#

• Extremely fast substring search

• Rare but high-reward for deep interviews

Manacher’s Algorithm#

• O(n) longest palindromic substring

📝 Must Do String Problems#

🔹 Level 1 – Easy#

1. Reverse string

2. Palindrome check

3. Count occurrences of characters

4. Remove duplicates

5. String compression

6. Leetcode 412. Fizz Buzz{:target=“_blank” rel=“noopener noreferrer”} - Solution

7. Leetcode 14. Longest Common Prefix{:target=“_blank” rel=“noopener noreferrer”} - Solution{:target=“_blank” rel=“noopener noreferrer”}

🔹 Level 2 – Medium#

1. Longest substring without repeating

2. Longest palindromic substring

3. Group anagrams

4. Valid parentheses

5. Multiply large numbers (string simulation)

6. Leetcode 271. Encode and Decode Strings{Premium Problem}{:target=“_blank” rel=“noopener noreferrer”} - My Leetcode Solution link{:target=“_blank” rel=“noopener noreferrer”}

   • If you can’t see the problem, Click Here

7. Leetcode 647. Palindromic Substrings{:target=“_blank” rel=“noopener noreferrer”} - My Leetcode Solution link{:target=“_blank” rel=“noopener noreferrer”}

8. Leetcode 5. Longest Palindromic Substring{:target=“_blank” rel=“noopener noreferrer”} - My Leetcode Solution link{:target=“_blank” rel=“noopener noreferrer”}

🔹 Level 3 – Hard#

1. Minimum window substring

2. Word break (DP + String)

3. Regular expression matching (DP)

4. Wildcard matching

5. KMP + Z-algorithm applications

6. Longest duplicate substring (binary search + hash)

7. Leetcode 647. Palindromic Substrings{:target=“_blank” rel=“noopener noreferrer”} - My Leetcode Solution link{:target=“_blank” rel=“noopener noreferrer”}

8. Leetcode 68. Text Justification{:target=“_blank” rel=“noopener noreferrer”} - My Leetcode Solution link{:target=“_blank” rel=“noopener noreferrer”}