DSA in JS

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1. 01 Two Sum: find indices of two numbers in an array that add up to a target, in O(n) using a hash map. Easy
2. 02 Valid Parentheses: determine if a string of brackets is balanced using a stack. Easy
3. 03 Merge Two Sorted Arrays/Lists in-place or into a new sorted structure. Easy
4. 04 Group Anagrams: group an array of strings into anagram clusters. Medium
5. 05 Longest Substring Without Repeating Characters using the sliding window technique. Medium
6. 06 Implement a binary search and explain its invariants and edge cases (off-by-one errors). Easy
7. 07 Detect a cycle in a linked list using Floyd's Tortoise and Hare algorithm. Medium
8. 08 Find the kth largest element in an array using a heap or quickselect. Medium
9. 09 Implement a trie (prefix tree) supporting insert, search, and startsWith. Hard
10. 10 Flatten a nested array (arbitrary depth) both iteratively and recursively. Medium
11. 11 Number of Islands: count connected components in a 2D grid using BFS/DFS. Medium
12. 12 Implement a debounced binary search suggestion box combining DSA + async concepts. Hard
13. 13 Find the longest common prefix among an array of strings. Easy
14. 14 Climbing Stairs / Fibonacci-style DP: count distinct ways to reach the top, with memoization. Easy
15. 15 Implement quicksort or mergesort from scratch and analyze time/space complexity. Medium
16. 16 Word Break: determine if a string can be segmented into dictionary words using DP. Medium
17. 17 Find all subsets (power set) of a given array using backtracking. Medium
18. 18 Implement a min-heap from scratch supporting insert and extract-min. Hard
19. 19 LRU Cache design and implementation combining Map + doubly linked list. Hard
20. 20 Product of Array Except Self without using division. Medium
21. 21 Implement a rate-limited queue processor respecting a max-requests-per-second constraint. Hard
22. 22 Serialize and deserialize a binary tree. Hard
23. 23 Find the median of two sorted arrays in better than O(n) time. Hard
24. 24 Implement a basic calculator that evaluates a string math expression with +,-,*,/ and parentheses. Hard
25. 25 Top K Frequent Elements using a hashmap and heap/bucket sort. Medium