JavaScript SDE-2 Practice Problems

A curated collection of JavaScript problems grouped by topic, designed for SDE-2 level interviews.

Each problem is located in the problems/ folder with its own test case in tests/.

---

📚 Grouped Problem List

Array

#	Problem	File
05	Find Largest Number in Array	05-find-largest-number-in-array.js
06	Remove Duplicates from Array	06-remove-duplicates-from-array.js
07	Element Frequency in Array	07-element-frequency-in-array.js
10	Flatten Nested Array	10-flatten-nested-array.js
11	Rotate Array by K Steps	11-rotate-array-by-k-steps.js
15	Move All Zeroes to End	15-move-all-zeroes-to-end.js
16	Merge Two Sorted Arrays	16-merge-two-sorted-arrays.js
17	All Pairs with Given Sum	17-all-pairs-with-given-sum.js
20	Product of Array Except Self	20-product-of-array-except-self.js
51	Find Intersection of Two Arrays	51-find-intersection-of-two-arrays.js
57	Count Occurrences of Element	57-count-occurrences-of-element.js
61	Majority Element	61-majority-element.js
71	Find Duplicates in Array	71-find-duplicates-in-array.js
72	Two Sum Problem	72-two-sum-problem.js
73	Three Sum Problem	73-three-sum-problem.js
99	Sort by Frequency	99-sort-by-frequency.js

Async

#	Problem	File
40	Promisify Callback	40-promisify-callback.js
41	Promise.all Polyfill	41-promise.all-polyfill.js
42	Retry Failed Fetch	42-retry-failed-fetch.js
43	Chain Async Operations	43-chain-async-operations.js
44	Timeout Wrapper for Promise	44-timeout-wrapper-for-promise.js
45	Sequential vs Parallel Promises	45-sequential-vs-parallel-promises.js

Backtracking

#	Problem	File
28	N-Queens Problem	28-n-queens-problem.js
29	Sudoku Solver	29-sudoku-solver.js

Binary Search

#	Problem	File
55	Find Peak Element	55-find-peak-element.js

Bit Manipulation

#	Problem	File
23	Count Set Bits	23-count-set-bits.js

DFS

#	Problem	File
74	Count Islands in Matrix	74-count-islands-in-matrix.js

DP

#	Problem	File
67	Word Break Problem	67-word-break-problem.js
68	Climb Stairs (Fibonacci)	68-climb-stairs-fibonacci.js
69	Coin Change	69-coin-change.js
70	Unique Paths in Grid	70-unique-paths-in-grid.js

Design

#	Problem	File
32	LRU Cache	32-lru-cache.js
46	Event Emitter	46-event-emitter.js
47	Rate Limiter	47-rate-limiter.js
48	Autocomplete with Trie	48-autocomplete-with-trie.js
49	Job Scheduler	49-job-scheduler.js
50	In-memory Key-Value Store	50-in-memory-key-value-store.js
82	Design Stack with Min	82-design-stack-with-min.js
83	Browser History Navigation	83-browser-history-navigation.js
84	LRU Cache with Doubly Linked List	84-lru-cache-with-doubly-linked-list.js

Functional

#	Problem	File
36	Custom Map Polyfill	36-custom-map-polyfill.js
37	Custom Reduce Polyfill	37-custom-reduce-polyfill.js
38	Debounce Implementation	38-debounce-implementation.js
39	Memoize Function	39-memoize-function.js
90	Throttle Implementation	90-throttle-implementation.js
91	Function Currying	91-function-currying.js
92	Custom Bind Polyfill	92-custom-bind-polyfill.js
93	Compose Function	93-compose-function.js

Graph

#	Problem	File
85	Clone Graph	85-clone-graph.js
86	Detect Cycle in Graph	86-detect-cycle-in-graph.js
87	Topological Sort	87-topological-sort.js
88	Dijkstra's Algorithm	88-dijkstra's-algorithm.js
89	A* Pathfinding	89-a*-pathfinding.js

Hash Map

#	Problem	File
12	Group Anagrams	12-group-anagrams.js

Looping

#	Problem	File
04	FizzBuzz	04-fizzbuzz.js

Map

#	Problem	File
33	Frequency Counter using Map	33-frequency-counter-using-map.js

Math

#	Problem	File
13	Missing Number from 1 to N	13-missing-number-from-1-to-n.js
21	Check Prime Number	21-check-prime-number.js
22	GCD and LCM	22-gcd-and-lcm.js
24	Armstrong Number	24-armstrong-number.js
96	Generate Random Hex Color	96-generate-random-hex-color.js
97	UUID Generator	97-uuid-generator.js
98	Binary to Decimal Converter	98-binary-to-decimal-converter.js

Matrix

#	Problem	File
58	Spiral Order Matrix	58-spiral-order-matrix.js
59	Transpose Matrix	59-transpose-matrix.js
66	Set Matrix Zeroes	66-set-matrix-zeroes.js

Object

#	Problem	File
31	Deep Clone Object	31-deep-clone-object.js
34	Group Objects by Key	34-group-objects-by-key.js
35	Deep Equality Check	35-deep-equality-check.js
95	Deep Freeze Object	95-deep-freeze-object.js

Recursion

#	Problem	File
03	Factorial of a Number	03-factorial-of-a-number.js
26	All Permutations of String	26-all-permutations-of-string.js
27	Tower of Hanoi	27-tower-of-hanoi.js
30	Power Set	30-power-set.js

Search

#	Problem	File
56	Binary Search Implementation	56-binary-search-implementation.js
60	Search in Rotated Sorted Array	60-search-in-rotated-sorted-array.js

Sliding Window

#	Problem	File
18	Longest Unique Substring	18-longest-unique-substring.js
65	Minimum Window Substring	65-minimum-window-substring.js

Stack

#	Problem	File
52	Check Balanced Parentheses	52-check-balanced-parentheses.js
53	Evaluate Reverse Polish Notation	53-evaluate-reverse-polish-notation.js

String

| # | Problem | File |string/ |--:|---------|------| | 01 | Reverse a String | 01-reverse-a-string.js | | 02 | Check if a String is Palindrome | 02-check-if-a-string-is-palindrome.js | | 08 | Anagram Check | 08-anagram-check.js | | 09 | Capitalize First Letter | 09-capitalize-first-letter.js | | 14 | First Non-Repeating Character | 14-first-non-repeating-character.js | | 19 | Is Subsequence | 19-is-subsequence.js | | 25 | Roman to Integer | 25-roman-to-integer.js | | 54 | Longest Common Prefix | 54-longest-common-prefix.js | | 62 | Zigzag Conversion | 62-zigzag-conversion.js | | 63 | String Compression | 63-string-compression.js | | 64 | Longest Palindromic Substring | 64-longest-palindromic-substring.js | | 94 | Parse Query String | 94-parse-query-string.js | | 101| Reverse All Strings of a Sentence | 101-reverse-all-strings.js |

Tree

#	Problem	File
75	Max Depth of Binary Tree	75-max-depth-of-binary-tree.js
76	Level Order Traversal	76-level-order-traversal.js
77	Binary Tree Inorder Traversal	77-binary-tree-inorder-traversal.js
78	Lowest Common Ancestor	78-lowest-common-ancestor.js
79	Validate Binary Search Tree	79-validate-binary-search-tree.js
80	Invert Binary Tree	80-invert-binary-tree.js
81	Serialize and Deserialize Tree	81-serialize-and-deserialize-tree.js

---

✅ How to Use

1. Install dependencies (for running tests):

   npm install

2. Solve problems inside the problems/ folder.

3. Add or review test cases in the tests/ folder.

4. Run tests using:

   npm test

Tests are powered by Jest.

---

💡 Contributions Welcome!

Feel free to fork and submit PRs with solutions or improvements.