Practice problems across 75+ categories
Practice problems frequently asked at Apple • 571 problems | 192 Easy | 283 Medium | 92 Hard
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 541 | Transform to Chessboard | Hard | ArrayMathBit Manipulation |
| 542 | Trapping Rain Water | Hard | ArrayTwo PointersDynamic Programming |
| 543 | Trapping Rain Water II | Hard | ArrayBreadth-First SearchHeap (Priority Queue) |
| 544 | Ugly Number | Easy | Math |
| 545 | Ugly Number II | Medium | Hash TableMathDynamic Programming |
| 546 | Uncommon Words from Two Sentences | Easy | Hash TableStringCounting |
| 547 | Uncrossed Lines | Medium | ArrayDynamic Programming |
| 548 | Undefined to Null | Medium | JavaScript |
| 549 | Unique Binary Search Trees II | Medium | Dynamic ProgrammingBacktrackingTree |
| 550 | Unique Orders and Customers Per Month | Easy | Database |
| 551 | Unique Paths II | Medium | ArrayDynamic ProgrammingMatrix |
| 552 | Unique Word Abbreviation | Medium | ArrayHash TableString |
| 553 | UTF-8 Validation | Medium | ArrayBit Manipulation |
| 554 | Valid Anagram | Easy | Hash TableStringSorting |
| 555 | Valid Palindrome | Easy | Two PointersString |
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