23 DSA Patterns

The extended list with three problems under each difficulty level (Easy, Medium, Hard) for each DSA pattern:

Disclaimer: All the problems links will redirect you to leetcode, few problems are only accessible for premium users on leetcode.

1. Sliding Window

No.	Problem	Level
1.	Maximum Sum of Two Non-Overlapping Subarrays	Easy
2.	Longest Substring Without Repeating Characters	Easy
3.	Grumpy Bookstore Owner	Easy
4.	Minimum Window Substring	Medium
5.	Longest Substring with At Least K Repeating Characters	Medium
6.	Permutation in String	Medium
7.	Substring with Concatenation of All Words	Hard
8.	Sliding Window Maximum	Hard
9.	Longest Substring with At Most Two Distinct Characters	Hard

2. Two Pointers

No.	Problem	Level
1.	Two Sum II – Input Array Is Sorted	Easy
2.	Remove Duplicates from Sorted Array	Easy
3.	Valid Palindrome II	Easy
4.	3Sum	Medium
5.	Container With Most Water	Medium
6.	Subarray Product Less Than K	Medium
7.	Trapping Rain Water	Hard
8.	4Sum	Hard
9.	Shortest Word Distance II	Hard

3. Fast & Slow Pointers

No.	Problem	Level
1.	Linked List Cycle	Easy
2.	Middle of the Linked List	Easy
3.	Happy Number	Easy
4.	Find the Duplicate Number	Medium
5.	Remove Linked List Elements	Medium
6.	Linked List Cycle II	Medium
7.	Palindrome Linked List	Hard
8.	Reorder List	Hard
9.	Split Linked List in Parts	Hard

4. Merge Intervals

No.	Problem	Level
1.	Merge Two Sorted Lists	Easy
2.	Interval List Intersections	Easy
3.	Minimum Number of Arrows to Burst Balloons	Easy
4.	Merge Intervals	Medium
5.	Insert Interval	Medium
6.	Meeting Rooms II	Medium
7.	Employee Free Time	Hard
8.	The Skyline Problem	Hard
9.	Minimum Cost to Hire K Workers	Hard

5. Cyclic Sort

No.	Problem	Level
1.	Find All Numbers Disappeared in an Array	Easy
2.	Find the Duplicate Number	Easy
3.	Find All Duplicates in an Array	Easy
4.	Set Mismatch	Medium
5.	First Missing Positive	Medium
6.	Missing Number	Medium
7.	First Missing Positive	Hard
8.	Find the Duplicate Number	Hard
9.	Find All Numbers Disappeared in an Array	Hard

6. In-place Reversal of a Linked List

No.	Problem	Level
1.	Reverse Linked List	Easy
2.	Reverse Linked List II	Easy
3.	Palindrome Linked List	Easy
4.	Reverse Nodes in k-Group	Medium
5.	Swap Nodes in Pairs	Medium
6.	Rotate List	Medium
7.	Reverse Nodes in k-Group	Hard
8.	Reverse Linked List II	Hard
9.	Rotate List	Hard

7. Tree BFS

No.	Problem	Level
1.	Binary Tree Level Order Traversal	Easy
2.	Binary Tree Level Order Traversal II	Easy
3.	Minimum Depth of Binary Tree	Easy
4.	Binary Tree Zigzag Level Order Traversal	Medium
5.	Binary Tree Right Side View	Medium
6.	Cousins in Binary Tree	Medium
7.	Word Ladder	Hard
8.	Cut Off Trees for Golf Event	Hard
9.	Binary Tree Maximum Path Sum	Hard

8. Tree DFS

No.	Problem	Level
1.	Path Sum	Easy
2.	Invert Binary Tree	Easy
3.	Diameter of Binary Tree	Easy
4.	Path Sum II	Medium
5.	Binary Tree Longest Consecutive Sequence	Medium
6.	Binary Tree Maximum Path Sum	Medium
7.	Binary Tree Cameras	Hard
8.	Binary Tree Maximum Path Sum	Hard
9.	Path Sum III	Hard

9. Two Heaps

No.	Problem	Level
1.	Last Stone Weight	Easy
2.	Kth Largest Element in a Stream	Easy
3.	Top K Frequent Elements	Easy
4.	Find Median from Data Stream	Medium
5.	Sliding Window Median	Medium
6.	IPO – LeetCode	Medium
7.	Minimum Cost to Connect Sticks	Hard
8.	The Skyline Problem	Hard
9.	Find Median from Data Stream	Hard

10. Subsets

No.	Problem	Level
1.	Subsets	Easy
2.	Combination Sum	Easy
3.	Permutations	Easy
4.	Subsets II	Medium
5.	Combination Sum II	Medium
6.	Permutations II	Medium
7.	Word Squares	Hard
8.	Palindrome Partitioning II	Hard
9.	Super Palindromes	Hard

11. Modified Binary Search

No.	Problem	Level
1.	Search Insert Position	Easy
2.	Guess Number Higher or Lower	Easy
3.	Find Smallest Letter Greater Than Target	Easy
4.	Search in Rotated Sorted Array	Medium
5.	Find Peak Element	Medium
6.	Search a 2D Matrix	Medium
7.	Median of Two Sorted Arrays	Hard
8.	Split Array Largest Sum	Hard
9.	Find Minimum in Rotated Sorted Array II	Hard

12. Top K Elements

No.	Problem	Level
1.	Kth Largest Element in a Stream	Easy
2.	Top K Frequent Elements	Easy
3.	Sort Characters By Frequency	Easy
4.	Kth Largest Element in an Array	Medium
5.	Task Scheduler	Medium
6.	Top K Frequent Words	Medium
7.	Smallest Range Covering Elements from K Lists	Hard
8.	Sliding Window Median	Hard
9.	Find Median from Data Stream	Hard

13. K-way Merge

No.	Problem	Level
1.	Merge Two Sorted Lists	Easy
2.	Merge Sorted Array	Easy
3.	Intersection of Two Arrays II	Easy
4.	Merge k Sorted Lists	Medium
5.	Kth Smallest Element in a Sorted Matrix	Medium
6.	Find K Pairs with Smallest Sums	Medium
7.	Smallest Range Covering Elements from K Lists	Hard
8.	Median of Two Sorted Arrays	Hard
9.	Split Array Largest Sum	Hard

14. Knapsack (Dynamic Programming)

No.	Problem	Level
1.	Climbing Stairs	Easy
2.	House Robber	Easy
3.	Partition Equal Subset Sum	Easy
4.	Partition Equal Subset Sum	Medium
5.	Coin Change	Medium
6.	Target Sum	Medium
7.	Target Sum	Hard
8.	Coin Change 2	Hard
9.	Wildcard Matching	Hard

15. Palindrome

No.	Problem	Level
1.	Valid Palindrome	Easy
2.	Valid Palindrome II	Easy
3.	Palindrome Linked List	Easy
4.	Longest Palindromic Substring	Medium
5.	Palindromic Substrings	Medium
6.	Palindrome Partitioning	Medium
7.	Palindrome Pairs	Hard
8.	Longest Palindromic Subsequence	Hard
9.	Palindrome Partitioning II	Hard

16. Topological Sort

No.	Problem	Level
1.	Course Schedule	Easy
2.	Course Schedule II	Easy
3.	Find Eventual Safe States	Easy
4.	Course Schedule II	Medium
5.	Alien Dictionary	Medium
6.	Minimum Height Trees	Medium
7.	Alien Dictionary	Hard
8.	Sequence Reconstruction	Hard
9.	Parallel Courses	Hard

17. Trie

No.	Problem	Level
1.	Implement Trie (Prefix Tree)	Easy
2.	Add and Search Word – Data structure design	Easy
3.	Design Add and Search Words Data Structure	Easy
4.	Word Search	Medium
5.	Word Search II	Medium
6.	Replace Words	Medium
7.	Design Search Autocomplete System	Hard
8.	Concatenated Words	Hard
9.	Longest Word in Dictionary through Deleting	Hard

18. Greedy Technique

No.	Problem	Level
1.	Assign Cookies	Easy
2.	Two City Scheduling	Easy
3.	Is Subsequence	Easy
4.	Jump Game	Medium
5.	Partition Labels	Medium
6.	Queue Reconstruction by Height	Medium
7.	Candy	Hard
8.	Minimum Number of Refueling Stops	Hard
9.	Minimum Cost to Hire K Workers	Hard

19. Backtracking

No.	Problem	Level	Resource
1.	Letter Combinations of a Phone Number	Easy
2.	Generate Parentheses	Easy	Solution
3.	Subsets	Easy
4.	Subsets II	Medium
5.	Combination Sum	Medium
6.	Permutations	Medium
7.	N-Queens	Hard
8.	Sudoku Solver	Hard
9.	Word Search II	Hard

20. Dynamic Programming

No.	Problem	Level
1.	House Robber	Easy
2.	Climbing Stairs	Easy
3.	Best Time to Buy and Sell Stock	Easy
4.	Longest Increasing Subsequence	Medium
5.	Longest Common Subsequence	Medium
6.	Coin Change	Medium
7.	Edit Distance	Hard
8.	Burst Balloons	Hard
9.	Regular Expression Matching	Hard

21. Monotonic Stack

No.	Problem	Level
1.	Next Greater Element I	Easy
2.	Next Greater Element II	Easy
3.	Remove All Adjacent Duplicates in String II	Easy
4.	Daily Temperatures	Medium
5.	Asteroid Collision	Medium
6.	Sum of Subarray Minimums	Medium
7.	Largest Rectangle in Histogram	Hard
8.	Trapping Rain Water	Hard
9.	Maximal Rectangle	Hard

22. Bitwise XOR

No.	Problem	Level
1.	Single Number	Easy
2.	Missing Number	Easy
3.	Number Complement	Easy
4.	Find the Duplicate Number	Medium
5.	Single Number II	Medium
6.	Maximum XOR of Two Numbers in an Array	Medium
7.	Find the Smallest Divisor Given a Threshold	Hard
8.	Maximum XOR of Two Numbers in an Array	Hard
9.	Concatenated Words	Hard

23. Island (Matrix Traversal) Pattern

No.	Problem	Level
1.	Flood Fill	Easy
2.	Max Area of Island	Easy
3.	Number of Enclaves	Easy
4.	Number of Islands	Medium
5.	Surrounded Regions	Medium
6.	Pacific Atlantic Water Flow	Medium
7.	Shortest Bridge	Hard
8.	Cut Off Trees for Golf Event	Hard
9.	Making A Large Island	Hard

This expanded list provides a well-rounded set of problems across different difficulty levels, allowing you to practice each DSA pattern progressively.

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