Coding Practice

Solve problems in the MyLoginn IDE — Python, JavaScript and SQL — with instant results on sample and hidden test cases. Earn XP for every first solve.

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Problem Set

Title	Tags	Acceptance	Difficulty
1. Two Sum	Array · Hash Map	—	Easy
2. Maximum Subarray Sum	Array · Dynamic Programming · Kadane	—	Medium
3. Binary Search	Binary Search · Array	—	Easy
4. Climbing Stairs	Dynamic Programming · Recursion	—	Easy
5. Coin Change	Dynamic Programming	—	Medium
6. Longest Increasing Subsequence	Dynamic Programming · Binary Search	—	Medium
7. Activity Selection	Greedy · Sorting	—	Medium
8. Longest Common Subsequence	Dynamic Programming · String	—	Medium
9. Edit Distance	Dynamic Programming · String	—	Hard
10. 0/1 Knapsack	Dynamic Programming	—	Hard
11. N-Queens Count	Backtracking	—	Hard
12. Valid Parentheses	Stack · String	—	Easy
13. Next Greater Element	Stack · Monotonic Stack	—	Medium
14. Sliding Window Maximum	Deque · Sliding Window	—	Hard
15. Element Frequency	Hash Map · Counting	—	Easy
16. Shortest Path in a Graph	Graph · BFS	—	Medium
17. Number of Islands	Graph · DFS · Matrix	—	Medium
18. Merge Intervals	Sorting · Intervals	—	Medium
19. Top K Frequent Elements	Hash Map · Sorting · Heap	—	Medium
20. Sum of Digits	Math	—	Easy
21. GCD and LCM	Math · Number Theory	—	Easy
22. Is It Prime?	Math · Primes	—	Easy
23. Count Primes	Sieve of Eratosthenes	—	Medium
24. Factorial Trailing Zeros	Math	—	Easy
25. Pascal's Triangle	Math · Array	—	Easy
26. nCr Modulo 1e9+7	Combinatorics · Modular Arithmetic	—	Medium
27. Palindrome Check	String · Two Pointers	—	Easy
28. Valid Anagram	String · Hash Map · Sorting	—	Easy
29. Reverse Words	String	—	Easy
30. String Compression	String · Run-Length Encoding	—	Easy
31. Caesar Cipher	String · Math	—	Easy
32. First Unique Character	String · Hash Map	—	Easy
33. Longest Palindromic Substring	String · Expand Around Center	—	Medium
34. Count Vowels and Consonants	String	—	Easy
35. FizzBuzz	Math · Simulation	—	Easy
36. Best Time to Buy and Sell Stock	Array · Greedy	—	Easy
37. Majority Element	Array · Boyer-Moore Voting	—	Easy
38. Move Zeroes	Array · Two Pointers	—	Easy
39. Rotate Array	Array	—	Easy
40. Trapping Rain Water	Two Pointers · Array	—	Hard
41. Product of Array Except Self	Array · Prefix Products	—	Medium
42. Missing Number	Math · Bit Manipulation	—	Easy
43. Word Frequency	String · Hash Map · Sorting	—	Easy
44. Set Operations	Set	—	Easy
45. Top Student	Dictionary · Sorting	—	Easy
46. snake_case to camelCase	String	—	Easy
47. Chunk an Array	Array	—	Easy
48. Sum of Array	Array	—	Easy
49. Minimum and Maximum	Array	—	Easy
50. Reverse an Array	Array · Two Pointers	—	Easy
51. Second Largest Distinct Element	Array	—	Easy
52. Count Even and Odd	Array	—	Easy
53. Prefix Sums	Array · Prefix Sum	—	Easy
54. Range Sum Queries	Prefix Sum	—	Medium
55. Left Rotation	Array	—	Easy
56. Remove Duplicates from Sorted Array	Two Pointers	—	Easy
57. Merge Two Sorted Arrays	Two Pointers · Merge	—	Easy
58. Negatives Before Positives	Array · Partition	—	Easy
59. Leaders in an Array	Array · Suffix Max	—	Easy
60. Equilibrium Index	Prefix Sum	—	Medium
61. Max Consecutive Ones	Array	—	Easy
62. Missing and Repeating	Array · Math	—	Medium
63. Best Subarray with Bounds	Kadane	—	Medium
64. Product Modulo	Modular Arithmetic	—	Easy
65. Pair with Given Difference	Hash Set	—	Medium
66. Count Pairs with Sum	Hash Map · Counting	—	Medium
67. Subarrays with Sum K	Prefix Sum · Hash Map	—	Medium
68. Longest Subarray with Sum K	Prefix Sum · Hash Map	—	Medium
69. Maximum Sum Window	Sliding Window	—	Easy
70. Shortest Subarray with Sum ≥ S	Sliding Window · Two Pointers	—	Medium
71. Count Inversions	Merge Sort · Divide and Conquer	—	Hard
72. Elements More Than n/3 Times	Counting	—	Medium
73. Stock Span	Monotonic Stack	—	Medium
74. Sort 0s, 1s and 2s	Dutch National Flag	—	Easy
75. Next Permutation	Permutation	—	Medium
76. Alternate Positive and Negative	Array	—	Medium
77. Find a Peak Element	Binary Search	—	Medium
78. Intersection of Two Arrays	Set	—	Easy
79. Union of Two Arrays	Set	—	Easy
80. Sort by Frequency	Sorting · Hash Map	—	Medium
81. First Repeating Element	Hash Map	—	Easy
82. Zig-Zag Arrangement	Greedy	—	Medium
83. Minimum Platforms	Sorting · Sweep Line	—	Medium
84. Chocolate Distribution	Sorting · Sliding Window	—	Easy
85. Maximum Product of Two	Array	—	Easy
86. Distinct Elements in Every Window	Sliding Window · Hash Map	—	Medium
87. Reverse a String	String	—	Easy
88. Count Letters, Digits and Spaces	String	—	Easy
89. Toggle Case	String	—	Easy
90. Count Words	String · Parsing	—	Easy
91. Capitalise Each Word	String	—	Easy
92. Remove Vowels	String	—	Easy
93. Character Frequency	Hash Map	—	Easy
94. Isogram Check	Set	—	Easy
95. Pangram Check	Set	—	Easy
96. Longest Word	String	—	Easy
97. Is It a Rotation?	String	—	Easy
98. Run-Length Decoding	String · Parsing	—	Easy
99. First Non-Repeating Character Index	Hash Map	—	Easy
100. Longest Common Prefix	String	—	Easy
101. Valid Palindrome (Letters and Digits)	Two Pointers	—	Easy
102. Longest Substring Without Repeats	Sliding Window	—	Medium
103. Count Anagram Groups	Hash Map · Sorting	—	Medium
104. Split into Balanced Strings	Greedy · Counting	—	Easy
105. String to Integer	Parsing	—	Medium
106. Roman to Integer	Hash Map	—	Easy
107. Integer to Roman	Greedy	—	Medium
108. Count Palindromic Substrings	Expand Around Centre	—	Medium
109. Most Frequent Character	Counting	—	Easy
110. Is Subsequence	Two Pointers	—	Easy
111. Reverse Only the Vowels	Two Pointers	—	Easy
112. Word Pattern	Hash Map · Bijection	—	Easy
113. Isomorphic Strings	Hash Map	—	Easy
114. Make Anagrams	Counting	—	Easy
115. Caesar Decoder	String · Modular Arithmetic	—	Easy
116. Longest Run After K Changes	Sliding Window	—	Medium
117. Minimum Window Containing All	Sliding Window	—	Hard
118. Decode Ways	Dynamic Programming	—	Medium
119. One Edit Away	Two Pointers	—	Medium
120. Zigzag Conversion	Simulation	—	Medium
121. Repeated Substring Pattern	String	—	Easy
122. Count and Say	Simulation	—	Medium
123. Valid Interleaving	Dynamic Programming	—	Hard
124. Count Binary Substrings	Counting	—	Easy
125. Factorial	Math · Big Integer	—	Easy
126. N-th Fibonacci Modulo	Fast Doubling · Matrix Power	—	Medium
127. Primes up to N	Sieve	—	Easy
128. Prime Factorisation	Factorisation	—	Easy
129. Number of Divisors	Divisors	—	Easy
130. Sum of Divisors	Divisors	—	Easy
131. Perfect Number	Divisors	—	Easy
132. Armstrong Number	Digits	—	Easy
133. Reverse an Integer	Digits	—	Easy
134. Palindrome Number	Digits	—	Easy
135. Digital Root	Digits · Modular Arithmetic	—	Easy
136. LCM of an Array	GCD · LCM	—	Easy
137. Modular Exponentiation	Fast Power	—	Medium
138. Modular Inverse	Extended Euclid · Fermat	—	Medium
139. Combinations nCr	Combinatorics	—	Easy
140. Catalan Number	Combinatorics	—	Medium
141. Digits of N!	Logarithms	—	Medium
142. Collatz Steps	Simulation	—	Easy
143. Decimal to Any Base	Number Bases	—	Easy
144. Any Base to Decimal	Number Bases	—	Easy
145. GCD of an Array	GCD	—	Easy
146. Euler's Totient	Totient	—	Medium
147. Sum of Two Squares	Two Pointers · Math	—	Medium
148. Goldbach Pair	Primes	—	Medium
149. Primes in a Range	Sieve · Prefix Sum	—	Medium
150. Pythagorean Triplets	Brute Force	—	Medium
151. Power of Two	Bits	—	Easy
152. Happy Number	Cycle Detection	—	Easy
153. N-th Ugly Number	Dynamic Programming	—	Medium
154. Excel Column Title	Number Bases	—	Easy
155. Excel Column Number	Number Bases	—	Easy
156. Integer Square Root	Binary Search	—	Easy
157. Integer K-th Root	Binary Search	—	Medium
158. Sum of All Digits 1..N	Digit DP	—	Hard
159. Sum of Squares 1..N	Formula	—	Easy
160. Leap Years in a Range	Inclusion–Exclusion	—	Easy
161. Clock Angle	Geometry	—	Easy
162. Triangle Type	Geometry	—	Easy
163. Polygon Area	Geometry · Shoelace	—	Medium
164. Points in Rectangle	Geometry	—	Easy
165. Sort an Array	Sorting	—	Easy
166. Sort in Descending Order	Sorting	—	Easy
167. Sort by Absolute Value	Custom Sort	—	Easy
168. Sort Words by Length	Custom Sort	—	Easy
169. First Position Not Less Than X	Binary Search	—	Easy
170. First and Last Occurrence	Binary Search	—	Easy
171. Search in Rotated Sorted Array	Binary Search	—	Medium
172. Minimum in Rotated Sorted Array	Binary Search	—	Medium
173. K-th Smallest Element	Sorting · Selection	—	Easy
174. Aggressive Cows	Binary Search on Answer	—	Hard
175. Allocate Books	Binary Search on Answer	—	Hard
176. Eating Speed	Binary Search on Answer	—	Medium
177. Median of Two Sorted Arrays	Binary Search · Merge	—	Hard
178. Count Elements ≤ X	Binary Search · Sorting	—	Easy
179. Triplets with Zero Sum	Two Pointers · Sorting	—	Medium
180. Pair Sum Closest to Target	Two Pointers	—	Medium
181. Contains Duplicate	Hash Set	—	Easy
182. Nearby Duplicate	Hash Map · Sliding Window	—	Easy
183. Longest Consecutive Sequence	Hash Set	—	Medium
184. Top K Frequent Words	Hash Map · Sorting	—	Medium
185. Valid Sudoku	Hash Set	—	Medium
186. Zero-Sum Subarray Exists?	Prefix Sum · Hash Set	—	Easy
187. Count Distinct Values	Hash Set	—	Easy
188. Four Arrays Zero Sum	Hash Map · Meet in the Middle	—	Medium
189. Pairs with Equal Digit Sum	Hash Map	—	Medium
190. Distinct Pairs with Sum	Hash Set	—	Medium
191. First Unique After Each Step	Queue · Hash Map	—	Medium
192. Stack Operations	Stack	—	Easy
193. Queue Operations	Queue	—	Easy
194. Min Stack	Stack · Design	—	Medium
195. Evaluate Postfix Expression	Stack	—	Medium
196. Infix to Postfix	Stack · Shunting Yard	—	Medium
197. Next Greater Element (Circular)	Monotonic Stack	—	Medium
198. Largest Rectangle in a Histogram	Monotonic Stack	—	Hard
199. Remove K Digits	Monotonic Stack · Greedy	—	Medium
200. Asteroid Collision	Stack · Simulation	—	Medium
201. Sliding Window Minimum	Deque	—	Medium
202. Decode String	Stack · Parsing	—	Medium
203. Simplify Unix Path	Stack	—	Medium
204. Minimum Brackets to Add	Counting	—	Medium
205. Longest Valid Parentheses	Stack	—	Hard
206. First Negative in Every Window	Queue · Sliding Window	—	Easy
207. Binary Numbers 1 to N	Queue	—	Easy
208. The Celebrity	Stack · Elimination	—	Medium
209. All Subsets	Backtracking · Bitmask	—	Medium
210. All Permutations	Backtracking	—	Medium
211. Unique Permutations	Backtracking	—	Medium
212. Combinations of K	Backtracking	—	Medium
213. Combination Sum	Backtracking	—	Medium
214. Subset Sum	Dynamic Programming	—	Medium
215. N-Queens Solutions Count	Backtracking	—	Hard
216. Word Search	DFS · Backtracking	—	Medium
217. Phone Keypad Combinations	Backtracking	—	Medium
218. Generate Parentheses	Backtracking	—	Medium
219. Tower of Hanoi	Recursion	—	Easy
220. Grid Paths	Combinatorics · Recursion	—	Easy
221. Palindrome Partitions	Backtracking	—	Medium
222. Gray Code	Bits · Recursion	—	Medium
223. Sudoku Solver	Backtracking	—	Hard
224. Rat in a Maze	Backtracking · DFS	—	Medium
225. House Robber	Dynamic Programming	—	Medium
226. House Robber (Circle)	Dynamic Programming	—	Medium
227. Min Cost Climbing Stairs	Dynamic Programming	—	Easy
228. Grid Paths with Obstacles	Dynamic Programming · Grid	—	Medium
229. Minimum Path Sum	Dynamic Programming · Grid	—	Medium
230. Triangle Minimum Path	Dynamic Programming	—	Medium
231. 0/1 Knapsack	Knapsack	—	Medium
232. Unbounded Knapsack	Knapsack	—	Medium
233. Coin Change — Number of Ways	Dynamic Programming · Counting	—	Medium
234. Longest Common Substring	Dynamic Programming	—	Medium
235. Longest Palindromic Subsequence	Dynamic Programming	—	Medium
236. Minimum Insertions for Palindrome	Dynamic Programming	—	Medium
237. Word Break	Dynamic Programming	—	Medium
238. Partition Equal Subset Sum	Knapsack	—	Medium
239. Target Sum with Signs	Dynamic Programming · Counting	—	Medium
240. Number of Longest Increasing Subsequences	Dynamic Programming	—	Hard
241. Maximum Product Subarray	Dynamic Programming	—	Medium
242. Jump Game	Greedy	—	Medium
243. Minimum Jumps	Greedy · BFS	—	Medium
244. Rod Cutting	Dynamic Programming	—	Medium
245. Egg Dropping	Dynamic Programming	—	Hard
246. Matrix Chain Multiplication	Interval DP	—	Hard
247. Ways to Make an Expression	Interval DP	—	Hard
248. Paint the Fence	Dynamic Programming · Counting	—	Medium
249. Count Binary Search Trees	Catalan	—	Medium
250. Dice Sum Ways	Dynamic Programming · Counting	—	Medium
251. Longest Bitonic Subsequence	Dynamic Programming	—	Medium
252. Largest Square of Ones	Dynamic Programming · Grid	—	Medium
253. Distinct Subsequence Count	Dynamic Programming · Counting	—	Hard
254. Wildcard Matching	Dynamic Programming	—	Hard
255. Regular Expression Matching	Dynamic Programming	—	Hard
256. Stock Trading with Cooldown	State Machine DP	—	Medium
257. Stock Trading with K Transactions	Dynamic Programming	—	Hard
258. Minimum Subset Difference	Knapsack	—	Medium
259. Count Subsets with Sum	Knapsack · Counting	—	Medium
260. Longest Arithmetic Subsequence	Dynamic Programming · Hash Map	—	Medium
261. Frog Jump with K	Dynamic Programming	—	Easy
262. Vacation Plan	Dynamic Programming	—	Medium
263. Perfect Squares	Dynamic Programming	—	Medium
264. Binary Strings Without Consecutive Ones	Dynamic Programming · Fibonacci	—	Easy
265. Domino Tiling 2×N	Dynamic Programming	—	Easy
266. Max Sum without Three Consecutive	Dynamic Programming	—	Medium
267. Maximum Meetings in One Room	Interval Scheduling	—	Easy
268. Fractional Knapsack	Greedy · Sorting	—	Easy
269. Minimum Notes (Indian Currency)	Greedy	—	Easy
270. Job Sequencing with Deadlines	Greedy · Sorting	—	Medium
271. Minimum Arrows to Burst Balloons	Intervals	—	Medium
272. Remove Overlapping Intervals	Intervals	—	Medium
273. Gas Station Circuit	Greedy	—	Medium
274. Candy Distribution	Greedy · Two Passes	—	Hard
275. Assign Cookies	Greedy · Sorting	—	Easy
276. Boats to Save People	Two Pointers · Greedy	—	Medium
277. Largest Number	Custom Sort	—	Medium
278. Minimum Sum from Digits	Greedy	—	Easy
279. Shortest Path (Unweighted)	BFS	—	Easy
280. Connected Components	DFS · Union-Find	—	Easy
281. Cycle in an Undirected Graph	Union-Find · DFS	—	Medium
282. Cycle in a Directed Graph	Topological Sort	—	Medium
283. Topological Order	Topological Sort	—	Medium
284. Shortest Path (Weighted)	Dijkstra	—	Medium
285. Minimum Spanning Tree	Kruskal · Union-Find	—	Medium
286. Is the Graph Bipartite?	BFS · Colouring	—	Medium
287. Diameter of a Tree	BFS · Trees	—	Medium
288. Tree Height from Parent Array	Trees	—	Easy
289. Friend Circles	DFS · Adjacency Matrix	—	Easy
290. Rotting Oranges	Multi-source BFS	—	Medium
291. Count Regions of Same Colour	DFS · Flood Fill	—	Easy
292. Word Ladder	BFS	—	Hard
293. Lowest Common Ancestor	Trees · LCA	—	Hard
294. Paths in a DAG	Topological Sort · DP	—	Medium
295. Knight's Shortest Path	BFS	—	Medium
296. Transpose a Matrix	Matrix	—	Easy
297. Add Two Matrices	Matrix	—	Easy
298. Multiply Two Matrices	Matrix	—	Medium
299. Rotate Matrix 90° Clockwise	Matrix	—	Medium
300. Spiral Order	Simulation	—	Medium
301. Spiral Matrix Generator	Simulation	—	Medium
302. Diagonal Difference	Matrix	—	Easy
303. Row with Maximum Sum	Matrix	—	Easy
304. Set Matrix Zeroes	Matrix	—	Medium
305. Search a Sorted Matrix	Staircase Search	—	Medium
306. Sub-matrix Sum Queries	2-D Prefix Sum	—	Medium
307. Island Perimeter	Grid	—	Easy
308. Negatives in a Sorted Matrix	Staircase	—	Easy
309. Toeplitz Matrix	Matrix	—	Easy
310. Game of Life — One Step	Simulation	—	Medium
311. Row with Most Ones	Binary Search	—	Easy
312. Count Set Bits	Bits	—	Easy
313. Set Bits for 0..N	Bits · DP	—	Easy
314. The Single Number	XOR	—	Easy
315. Single Number Among Triples	Bits	—	Medium
316. Reverse Bits	Bits	—	Easy
317. Hamming Distance	XOR	—	Easy
318. Total Hamming Distance	Bits · Counting	—	Medium
319. Find the Duplicate Number	XOR · Cycle Detection	—	Medium
320. Sum of All Subset XORs	Bits · Combinatorics	—	Medium
321. Bitwise AND of a Range	Bits	—	Medium
322. Power of Four	Bits	—	Easy
323. Maximum XOR of Two Numbers	Trie · Bits	—	Hard
324. Bits to Flip	XOR	—	Easy
325. Two Numbers with Odd Counts	XOR	—	Medium
326. Grade Calculator	Conditionals	—	Easy
327. Electricity Bill	Conditionals · Slabs	—	Easy
328. Loan EMI	Formula	—	Medium
329. Day of the Week	Calendar · Zeller	—	Medium
330. Days Between Dates	Calendar	—	Medium
331. 12-Hour to 24-Hour Time	Parsing	—	Easy
332. Seconds to H:M:S	Arithmetic	—	Easy
333. Tic-Tac-Toe Winner	Simulation	—	Easy
334. ATM Withdrawal	Conditionals	—	Easy
335. Parking Fee	Ceil Division	—	Easy
336. Vending Machine Change	Greedy	—	Easy
337. Bank Account Statement	Simulation	—	Medium
338. Library Fine	Conditionals · Dates	—	Easy
339. Password Strength	Validation	—	Easy
340. Validate an IPv4 Address	Parsing · Validation	—	Medium
341. Validate an Email Address	Validation	—	Medium
342. Minesweeper Numbers	Grid	—	Medium
343. Elevator Travel	Simulation	—	Easy
344. Waiting Time at a Counter	Simulation	—	Medium
345. Traffic Light Colour	Modular Arithmetic	—	Easy
346. Word Wrap	Greedy	—	Medium
347. Centre the Text	Formatting	—	Easy
348. Text Histogram	Counting	—	Easy
349. Running Median	Heaps	—	Hard
350. LRU Cache	Design · Linked Hash Map	—	Medium
351. Snakes and Ladders	BFS	—	Hard
352. Bowling Score	Simulation	—	Hard
353. Number to Words	Recursion · Formatting	—	Hard
354. Basic Calculator	Parsing · Stack	—	Hard
355. Inventory Orders	Hash Map · Simulation	—	Medium
356. Rainfall Statistics	Aggregation	—	Easy
357. Cinema Seat Booking	Simulation	—	Medium
358. Temperature Converter	Formula	—	Easy
359. Shopping Cart Total	Arithmetic	—	Easy
360. Robot Moves	Simulation	—	Easy
361. Attendance Shortfall	Math	—	Easy
362. Lottery Matches	Set	—	Easy
363. Reverse a Linked List	Linked List	—	Easy
364. Middle of a Linked List	Two Pointers	—	Easy
365. Remove N-th Node from End	Two Pointers	—	Medium
366. Merge Two Sorted Lists	Linked List · Merge	—	Easy
367. Palindrome Linked List	Two Pointers	—	Easy
368. Remove Duplicates from Sorted List	Linked List	—	Easy
369. Rotate List Right	Linked List	—	Medium
370. Add Two Numbers as Lists	Linked List · Math	—	Medium
371. Partition List	Linked List	—	Medium
372. Odd-Even Linked List	Linked List	—	Medium
373. Swap Nodes in Pairs	Linked List	—	Medium
374. Reverse Nodes in K-Groups	Linked List	—	Hard
375. Inorder Traversal	Binary Tree · DFS	—	Easy
376. Preorder Traversal	Binary Tree · DFS	—	Easy
377. Postorder Traversal	Binary Tree · DFS	—	Easy
378. Level Order by Lines	BFS	—	Easy
379. Zigzag Level Order	BFS	—	Medium
380. Maximum Depth of a Binary Tree	DFS	—	Easy
381. Minimum Depth	BFS	—	Easy
382. Count and Sum of Nodes	Traversal	—	Easy
383. Count Leaves	Traversal	—	Easy
384. Symmetric Tree	Recursion	—	Easy
385. Height-Balanced Tree	DFS	—	Easy
386. Diameter of a Binary Tree	DFS	—	Easy
387. Root-to-Leaf Path Sum	DFS	—	Easy
388. Validate a BST	BST · Inorder	—	Medium
389. K-th Smallest in a BST	BST · Inorder	—	Medium
390. LCA in a BST	BST	—	Easy
391. Build a BST by Insertion	BST	—	Easy
392. Range Sum of a BST	BST · DFS	—	Easy
393. Right Side View	BFS	—	Medium
394. Left Side View	BFS	—	Easy
395. Level Sums and Widest Level	BFS	—	Medium
396. Same Tree	Recursion	—	Easy
397. K Largest Elements	Heap	—	Easy
398. Merge K Sorted Lists	Heap · Merge	—	Hard
399. Connect Ropes at Minimum Cost	Heap · Greedy	—	Medium
400. K-th Largest in a Stream	Heap	—	Medium
401. Task Scheduler	Greedy · Counting	—	Medium
402. Container With Most Water	Two Pointers	—	Medium
403. Two Sum II (Sorted Input)	Two Pointers	—	Medium
404. 3Sum Closest	Two Pointers · Sorting	—	Medium
405. Remove Element	Two Pointers	—	Easy
406. Squares of a Sorted Array	Two Pointers	—	Easy
407. Palindrome After One Deletion	Two Pointers	—	Easy
408. Backspace String Compare	Stack · Two Pointers	—	Easy
409. Longest Mountain	Two Pointers · DP	—	Medium
410. Windows With Average ≥ Threshold	Sliding Window	—	Medium
411. Max Consecutive Ones With K Flips	Sliding Window	—	Medium
412. Fruit Into Baskets	Sliding Window · Hash Map	—	Medium
413. Subarray Product Less Than K	Sliding Window	—	Medium
414. Subarrays With Exactly K Odd Numbers	Prefix Sum · Hash Map	—	Medium
415. Binary Subarrays With Sum	Prefix Sum	—	Medium
416. Longest Substring With K Distinct Characters	Sliding Window	—	Medium
417. Permutation in String	Sliding Window	—	Medium
418. Find All Anagrams in a String	Sliding Window	—	Medium
419. Maximum Vowels in a Substring of Length K	Sliding Window	—	Medium
420. Grumpy Bookstore Owner	Sliding Window	—	Medium
421. Maximum Points From Cards	Sliding Window · Prefix Sum	—	Medium
422. Subarray Sums Divisible by K	Prefix Sum · Modulo	—	Medium
423. Longest Equal 0s and 1s	Prefix Sum · Hash Map	—	Medium
424. Longest Ones After Deleting One Element	Sliding Window	—	Medium
425. Insert Interval	Intervals	—	Medium
426. Interval List Intersections	Intervals · Two Pointers	—	Medium
427. Can Attend All Meetings	Intervals · Sorting	—	Easy
428. Summary Ranges	Array	—	Easy
429. Missing Ranges	Array	—	Easy
430. Find All Duplicates	Array	—	Medium
431. First Missing Positive	Array · Cyclic Sort	—	Hard
432. Find All Missing Numbers	Array	—	Easy
433. Sort Array by Parity (Stable)	Array	—	Easy
434. Relative Sort Array	Counting Sort	—	Easy
435. H-Index	Sorting	—	Medium
436. Array Partition (Max Sum of Pair Minimums)	Sorting · Greedy	—	Easy
437. Maximum Gap	Sorting	—	Medium
438. K-th Missing Positive Number	Binary Search	—	Easy
439. Range Updates With a Difference Array	Prefix Sum	—	Medium
440. Car Pooling	Prefix Sum · Simulation	—	Medium
441. Corporate Flight Bookings	Prefix Sum	—	Medium
442. Valid Triangle Number	Two Pointers · Sorting	—	Medium
443. Minimum Moves to Equal Elements	Math	—	Medium
444. Minimum Moves to Equal Elements II	Median	—	Medium
445. Longest Harmonious Subsequence	Hash Map	—	Easy
446. Degree of an Array	Hash Map	—	Easy
447. Number of Good Pairs	Counting	—	Easy
448. Kids With the Greatest Number of Candies	Array	—	Easy
449. Shuffle the Array	Array	—	Easy
450. How Many Numbers Are Smaller	Counting Sort	—	Easy
451. Lemonade Change	Greedy · Simulation	—	Easy
452. Poison Duration	Simulation	—	Easy
453. Can Place Flowers	Greedy	—	Easy
454. Distribute Candies	Hash Set	—	Easy
455. Maximum Units on a Truck	Greedy · Sorting	—	Easy
456. Minimum Cost to Move Chips	Parity	—	Easy
457. Two City Scheduling	Greedy · Sorting	—	Medium
458. Partition Labels	Greedy	—	Medium
459. Queue Reconstruction by Height	Greedy · Sorting	—	Medium
460. Largest Perimeter Triangle	Sorting · Greedy	—	Easy
461. Richest Customer Wealth	Matrix	—	Easy
462. Ransom Note	Counting	—	Easy
463. Jewels and Stones	Hash Set	—	Easy
464. Uncommon Words From Two Sentences	Hash Map	—	Easy
465. Custom Sort String	Sorting	—	Medium
466. Longest Palindrome You Can Build	Counting	—	Easy
467. Determine if Two Strings Are Close	Counting	—	Medium
468. Maximum Number of Balloons	Counting	—	Easy
469. Bulls and Cows	Counting	—	Medium
470. Find the Difference	Bit Manipulation · Counting	—	Easy
471. Add Binary	Math	—	Easy
472. Add Strings	Math	—	Easy
473. Multiply Strings	Math	—	Medium
474. Compare Version Numbers	Parsing	—	Medium
475. Length of Last Word	String	—	Easy
476. License Key Formatting	String	—	Easy
477. Detect Capital	String	—	Easy
478. Student Attendance Record	String	—	Easy
479. Robot Return to Origin	Simulation	—	Easy
480. Shortest Distance to a Character	Two Pass	—	Easy
481. Reverse Each Word	String	—	Easy
482. Reverse String II	String	—	Easy
483. Defang an IP Address	String	—	Easy
484. Final Value After Operations	Simulation	—	Easy
485. Goal Parser Interpretation	String	—	Easy
486. Count Consistent Strings	Hash Set	—	Easy
487. Steps to Reduce a Number to Zero	Simulation · Bit Manipulation	—	Easy
488. Water Bottles	Simulation	—	Easy
489. Bulb Switcher	Math	—	Medium
490. Broken Calculator	Greedy	—	Medium
491. Integer Replacement	Greedy · Bit Manipulation	—	Medium
492. Valid Perfect Square	Binary Search	—	Easy
493. Arranging Coins	Math · Binary Search	—	Easy
494. Power of Three	Math	—	Easy
495. Maximum 69 Number	Greedy	—	Easy
496. Self-Dividing Numbers	Math	—	Easy
497. N-th Tribonacci Number	DP	—	Easy
498. Count Odd Numbers in a Range	Math	—	Easy
499. Product Minus Sum of Digits	Math	—	Easy
500. Nim Game	Game Theory	—	Easy
501. High EarnersSQL	SELECT · WHERE · ORDER BY	—	Easy
502. Employees per DepartmentSQL	GROUP BY · COUNT	—	Easy
503. Second Highest SalarySQL	Subquery · MAX	—	Medium
504. Employee with DepartmentSQL	JOIN	—	Easy
505. Customers Who Never OrderedSQL	LEFT JOIN · NULL	—	Easy
506. Total Spent per CustomerSQL	JOIN · GROUP BY · SUM	—	Medium
507. Duplicate EmailsSQL	GROUP BY · HAVING	—	Easy
508. Above Department AverageSQL	Correlated Subquery	—	Medium
509. Top Earner per DepartmentSQL	Window Functions · RANK	—	Hard
510. Running Total of OrdersSQL	Window Functions · SUM OVER	—	Hard
511. Managers with Two or More ReportsSQL	Self Join · GROUP BY	—	Medium
512. Departments with No EmployeesSQL	NOT EXISTS · LEFT JOIN	—	Easy
513. All StudentsSQL	SELECT	—	Easy
514. Students from ChennaiSQL	WHERE	—	Easy
515. Missing CitySQL	NULL	—	Easy
516. Students per ClassSQL	GROUP BY	—	Easy
517. Average Score per SubjectSQL	JOIN · AVG	—	Easy
518. Total Marks per StudentSQL	JOIN · SUM	—	Medium
519. Topper in Each SubjectSQL	Window Functions	—	Hard
520. Students Without MarksSQL	LEFT JOIN	—	Easy
521. Assign GradesSQL	CASE	—	Medium
522. Passed Every Subject TakenSQL	HAVING · MIN	—	Medium
523. Rank Students in ClassSQL	Window Functions · DENSE_RANK	—	Hard
524. Youngest StudentSQL	ORDER BY · LIMIT	—	Easy
525. Born in 2010SQL	Dates · LIKE	—	Easy
526. Names Starting with a VowelSQL	LIKE · SUBSTR	—	Easy
527. Above the School AverageSQL	Subquery	—	Medium
528. Books by an AuthorSQL	WHERE	—	Easy
529. Books per GenreSQL	GROUP BY	—	Easy
530. Currently Borrowed BooksSQL	JOIN · NULL	—	Easy
531. Most Borrowed BookSQL	GROUP BY · ORDER BY	—	Medium
532. Books Never BorrowedSQL	NOT EXISTS	—	Easy
533. Loan DurationsSQL	Dates · julianday	—	Medium
534. Loans per MemberSQL	LEFT JOIN · COUNT	—	Medium
535. Authors with Several BooksSQL	HAVING	—	Easy
536. Classic BooksSQL	WHERE · BETWEEN	—	Easy
537. Available CopiesSQL	Subquery · COALESCE	—	Hard
538. Members Who Joined in 2024SQL	Dates	—	Easy
539. First Loan of Each MemberSQL	Window Functions · ROW_NUMBER	—	Hard
540. Salary BandsSQL	CASE · GROUP BY	—	Medium
541. Department PayrollSQL	JOIN · SUM	—	Easy
542. Recent HiresSQL	Dates	—	Easy
543. Employee and ManagerSQL	Self Join · LEFT JOIN	—	Medium
544. Third Highest SalarySQL	DISTINCT · LIMIT OFFSET	—	Medium
545. Share of Department PayrollSQL	Window Functions	—	Hard
546. Email DomainsSQL	String Functions	—	Medium
547. Monthly RevenueSQL	Dates · GROUP BY	—	Medium
548. Orders by CitySQL	JOIN · GROUP BY	—	Easy
549. Customer with the Largest OrderSQL	Subquery	—	Easy
550. Repeat CustomersSQL	HAVING	—	Easy
551. Order vs Previous OrderSQL	Window Functions · LAG	—	Hard
552. Revenue Share by CustomerSQL	Subquery	—	Medium

552 of 552 problems

Coding Practice

Practice Skills

Problem Set