| 401. Binary Watch | Solution | Solve | Easy | | |
| 402. Remove K Digits | Solution | Solve | Medium | | |
| 403. Frog Jump | Solution | Solve | Hard | | |
| 404. Sum of Left Leaves | Solution | Solve | Easy | | |
| 405. Convert a Number to Hexadecimal | Solution | Solve | Easy | | |
| 406. Queue Reconstruction by Height | Solution | Solve | Medium | | |
| 407. Trapping Rain Water II | Solution | Solve | Hard | | |
| 408. Valid Word Abbreviation | Solution | Solve | Easy | | |
| 409. Longest Palindrome | Solution | Solve | Easy | | |
| 410. Split Array Largest Sum | Solution | Solve | Hard | | |
| 411. Minimum Unique Word Abbreviation | Solution | Solve | Hard | | |
| 412. Fizz Buzz | Solution | Solve | Easy | | |
| 413. Arithmetic Slices | Solution | Solve | Medium | | |
| 414. Third Maximum Number | Solution | Solve | Easy | | |
| 415. Add Strings | Solution | Solve | Easy | | |
| 416. Partition Equal Subset Sum | Solution | Solve | Medium | | |
| 417. Pacific Atlantic Water Flow | Solution | Solve | Medium | | |
| 418. Sentence Screen Fitting | Solution | Solve | Medium | | |
| 419. Battleships in a Board | Solution | Solve | Medium | | |
| 420. Strong Password Checker | Solution | Solve | Hard | | |
| 421. Maximum XOR of Two Numbers in an Array | Solution | Solve | Medium | | |
| 422. Valid Word Square | Solution | Solve | Easy | | |
| 423. Reconstruct Original Digits from English | Solution | Solve | Medium | | |
| 424. Longest Repeating Character Replacement | Solution | Solve | Medium | | |
| 425. Word Squares | Solution | Solve | Hard | | |
| 426. Convert Binary Search Tree to Sorted Doubly Linked List | Solution | Solve | Medium | | |
| 427. Construct Quad Tree | Solution | Solve | Medium | | |
| 428. Serialize and Deserialize N-ary Tree | Solution | Solve | Hard | | |
| 429. N-ary Tree Level Order Traversal | Solution | Solve | Medium | | |
| 430. Flatten a Multilevel Doubly Linked List | Solution | Solve | Medium | | |
| 431. Encode N-ary Tree to Binary Tree | Solution | Solve | Hard | - | |
| 432. All O`one Data Structure | Solution | Solve | Hard | | |
| 433. Minimum Genetic Mutation | Solution | Solve | Medium | | |
| 434. Number of Segments in a String | Solution | Solve | Easy | | |
| 435. Non-overlapping Intervals | Solution | Solve | Medium | | |
| 436. Find Right Interval | Solution | Solve | Medium | | |
| 437. Path Sum III | Solution | Solve | Medium | | |
| 438. Find All Anagrams in a String | Solution | Solve | Medium | | |
| 439. Ternary Expression Parser | Solution | Solve | Medium | | |
| 440. K-th Smallest in Lexicographical Order | Solution | Solve | Hard | | |
| 441. Arranging Coins | Solution | Solve | Easy | | |
| 442. Find All Duplicates in an Array | Solution | Solve | Medium | | |
| 443. String Compression | Solution | Solve | Medium | | |
| 444. Sequence Reconstruction | Solution | Solve | Medium | | |
| 445. Add Two Numbers II | Solution | Solve | Medium | | |
| 446. Arithmetic Slices II - Subsequence | Solution | Solve | Hard | | |
| 447. Number of Boomerangs | Solution | Solve | Medium | | |
| 448. Find All Numbers Disappeared in an Array | Solution | Solve | Easy | | |
| 449. Serialize and Deserialize BST | Solution | Solve | Medium | | |
| 450. Delete Node in a BST | Solution | Solve | Medium | | |
