Apple Coding Interview Questions
32 Apple coding interview problems with full optimal solutions — 11 easy, 19 medium, 2 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an Apple interviewer values, and a FAQ section.
Showing 19 problems of 32
- #25mediumfoundational
25. Find Minimum in Rotated Sorted Array
Find the minimum element in a rotated sorted array in O(log n) — Apple asks this to test whether you can adapt binary search when invariants are partially broken, a skill directly applicable to finding pivot points in macOS system log timestamps.
- #26mediumfoundational
26. Number of Islands
Count connected land regions in a binary grid using BFS/DFS — Apple applies this grid-traversal pattern to UI layout engines that must identify distinct content regions on a display, and to Maps clustering connected geographic tiles.
- #27mediumfoundational
27. Course Schedule
Detect circular dependencies in a directed graph — Apple's Xcode build system and Swift Package Manager use topological sort to resolve framework dependency graphs; cycle detection is the first thing that must work correctly before any build starts.
- #28mediumfoundational
28. Validate Binary Search Tree
Verify that every node in a binary tree satisfies the full BST invariant — Apple's file system and UI accessibility tree code depends on validated sorted structures, making this a core screening question for roles touching CoreData or UIAccessibility.
- #29mediumfoundational
29. Decode Ways
Count all valid decodings of a digit string where 1-26 map to A-Z — Apple uses this DP pattern to evaluate how engineers reason about combinatorial text-parsing states, directly analogous to the multi-codepoint emoji rendering decisions in iMessage.
- #30mediumfoundational
30. Rotate Image
Rotate an n×n matrix 90 degrees clockwise in-place — Apple's AVFoundation and Photos frameworks rotate CVPixelBuffer image data without allocating extra memory on memory-constrained iPhones, making this in-place matrix transformation a consistent favorite for Camera and Vision team interviews.
- #31mediumfoundational
31. Kth Largest Element in an Array
Find the kth largest element without full sorting — Apple Fitness+ and HealthKit stream millions of events and must surface top-k rankings in real time; this heap/quickselect problem is a direct analog of that competitive-leaderboard challenge.
- #2mediumfrequently asked
2. Add Two Numbers
Add Two Numbers is Apple's linked-list-as-digits arithmetic question. Walk both lists in parallel, adding digit + digit + carry, allocate a new node per output digit, and handle different lengths and a possible trailing carry. The dummy-head trick keeps the code tidy.
4 free resourcesSolve → - #3mediumfoundational
3. Longest Substring Without Repeating Characters
Longest Substring Without Repeating Characters is the canonical sliding-window question and Apple's most-repeated string medium. Expand the right pointer; when a duplicate appears, jump the left pointer to last_index_of_dup + 1. The hash-map-of-char-to-last-index variant is what Apple grades on.
4 free resourcesSolve → - #7mediumfrequently asked
7. Reverse Integer
Reverse Integer is Apple's deceptively-simple overflow-detection question. The reversal loop is three lines; the real challenge is detecting 32-bit overflow BEFORE it happens. Apple grades on whether you remember -2^31 to 2^31 - 1 and check the bound on every digit append.
4 free resourcesSolve → - #8mediumfrequently asked
8. String to Integer (atoi)
String to Integer (atoi) is Apple's adversarial parsing question. Six precise rules — skip whitespace, read optional sign, read digits, clamp to 32-bit — and you must handle every weird input the interviewer throws at you. Apple grades on edge-case coverage, not on the parse loop itself.
4 free resourcesSolve → - #15mediumfrequently asked
15. 3Sum
3Sum is Apple's introduction to fix-one-then-two-pointer pattern. Sort the array, fix nums[i] as the anchor, then run a two-pointer sweep for the other two values that sum to -nums[i]. The duplicate-skipping is the bug surface Apple specifically grades on.
4 free resourcesSolve → - #102mediumfrequently asked
102. Binary Tree Level Order Traversal
Binary Tree Level Order Traversal is Apple's canonical BFS-on-a-tree question. Process the queue one level at a time by snapshotting its size at the start of each iteration. Apple grades on whether you remember the size snapshot — most candidates accidentally bleed levels together.
4 free resourcesSolve → - #146mediumfrequently asked
146. LRU Cache
LRU Cache is Apple's flagship data-structure design medium. The answer is a hash map for O(1) lookup plus a doubly linked list for O(1) move-to-front. Apple specifically grades on whether you handle the pointer surgery without leaving a dangling neighbor.
4 free resourcesSolve → - #198mediumfrequently asked
198. House Robber
House Robber is Apple's clean 1D DP medium. dp[i] = max(dp[i-1], dp[i-2] + nums[i]) — either skip this house or take it plus the best up to two back. Apple grades on whether you can derive that recurrence on the spot and reduce to O(1) space.
4 free resourcesSolve → - #211mediumfrequently asked
211. Design Add and Search Words Data Structure
Design Add and Search Words Data Structure is Apple's go-to trie design medium. Add inserts a word normally; search supports '.' as a wildcard that matches any single character. The wildcard turns the search into a tiny DFS down every matching child node.
4 free resourcesSolve → - #236mediumfrequently asked
236. Lowest Common Ancestor of a Binary Tree
Lowest Common Ancestor is Apple's elegant tree recursion medium. The clean answer is dual: 'return p or q if found, else return whichever subtree returned non-null — if both subtrees return non-null, this node is the LCA.' Five lines that make Apple interviewers smile.
4 free resourcesSolve → - #238mediumfrequently asked
238. Product of Array Except Self
Product of Array Except Self is Apple's beloved 'no division' question. Two passes — left-products then right-products into the same output array — gives O(n) time with O(1) extra space. Apple grades on whether you avoid division entirely and handle the multi-zero case.
4 free resourcesSolve → - #322mediumfrequently asked
322. Coin Change
Coin Change is Apple's go-to unbounded-knapsack DP medium. dp[i] = min coins to make amount i. For each i, try every coin and take the minimum. Apple is grading whether you can write the recurrence AND explain why the greedy (take the largest coin) does not work on arbitrary denominations.
4 free resourcesSolve →
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