301 
Remove Invalid Parentheses 
Hard 

303 
Range Sum Query  Immutable 
Easy 

304 
Range Sum Query 2D  Immutable 
Medium 

306 
Additive Number 
Medium 

307 
Range Sum Query  Mutable 
Medium 

309 
Best Time to Buy and Sell Stock with Cooldown 
Medium 

310 
Minimum Height Trees 
Medium 

312 
Burst Balloons 
Hard 

313 
Super Ugly Number 
Medium 

315 
Count of Smaller Numbers After Self 
Hard 

316 
Remove Duplicate Letters 
Medium 

318 
Maximum Product of Word Lengths 
Medium 

319 
Bulb Switcher 
Medium 

322 
Coin Change 
Medium 

323 
Number of Connected Components in an Undirected Graph 
Medium 

324 
Wiggle Sort II 
Medium 

326 
Power of Three 
Easy 

327 
Count of Range Sum 
Hard 

328 
Odd Even Linked List 
Medium 

329 
Longest Increasing Path in a Matrix 
Hard 

330 
Patching Array 
Hard 

331 
Verify Preorder Serialization of a Binary Tree 
Medium 

332 
Reconstruct Itinerary 
Medium 

333 
Largest BST Subtree 
Medium 
Tree

334 
Increasing Triplet Subsequence 
Medium 

335 
Self Crossing 
Hard 

336 
Palindrome Pairs 
Hard 

337 
House Robber III 
Medium 
Tree

Depthfirst Search

338 
Counting Bits 
Medium 

341 
Flatten Nested List Iterator 
Medium 

342 
Power of Four 
Easy 

343 
Integer Break 
Medium 

344 
Reverse String 
Easy 

345 
Reverse Vowels of a String 
Easy 

347 
Top K Frequent Elements 
Medium 

349 
Intersection of Two Arrays 
Easy 

350 
Intersection of Two Arrays II 
Easy 

352 
Data Stream as Disjoint Intervals 
Hard 

354 
Russian Doll Envelopes 
Hard 

355 
Design Twitter 
Medium 

357 
Count Numbers with Unique Digits 
Medium 

365 
Water and Jug Problem 
Medium 

366 
Find Leaves of Binary Tree 
Medium 
Tree

Depthfirst Search

367 
Valid Perfect Square 
Easy 

368 
Largest Divisible Subset 
Medium 

371 
Sum of Two Integers 
Medium 

372 
Super Pow 
Medium 

373 
Find K Pairs with Smallest Sums 
Medium 

374 
Guess Number Higher or Lower 
Easy 

375 
Guess Number Higher or Lower II 
Medium 

376 
Wiggle Subsequence 
Medium 

377 
Combination Sum IV 
Medium 

378 
Kth Smallest Element in a Sorted Matrix 
Medium 

380 
Insert Delete GetRandom O(1) 
Medium 

381 
Insert Delete GetRandom O(1)  Duplicates allowed 
Hard 

382 
Linked List Random Node 
Medium 

383 
Ransom Note 
Easy 

384 
Shuffle an Array 
Medium 

385 
Mini Parser 
Medium 

386 
Lexicographical Numbers 
Medium 

387 
First Unique Character in a String 
Easy 

388 
Longest Absolute File Path 
Medium 

389 
Find the Difference 
Easy 

390 
Elimination Game 
Medium 

391 
Perfect Rectangle 
Hard 

392 
Is Subsequence 
Easy 

393 
UTF8 Validation 
Medium 

394 
Decode String 
Medium 

395 
Longest Substring with At Least K Repeating Characters 
Medium 

396 
Rotate Function 
Medium 

397 
Integer Replacement 
Medium 

398 
Random Pick Index 
Medium 

399 
Evaluate Division 
Medium 

400 
Nth Digit 
Medium 
