Interview questions

Avoid Flood in The City

Assign dry operations on zero days so that no lake is rained on while already full: given a sequence where rains[i]>0 fills a lake and…

Companies: MongoDB

Array · Binary Search · Greedy · Hash Table

Beautiful Arrangement

Count the permutations of 1..n such that for every position i, either perm[i] is divisible by i or i is divisible by perm[i]. With n…

Companies: Rippling

Array · Backtracking · Bit Manipulation · Bitmask

Binary Searchable Numbers in an Unsorted Array

Given an unsorted array, count the elements that are "binary searchable" — values that would be found by standard binary search without sorting, meaning every…

Companies: Uber

Array · Binary Search · Monotonic Stack · Stack

Block Placement Queries

Support inserting obstacles at points on the nonnegative number line and, for each query, determine whether there exists any obstacle-free interval of length >= sz…

Companies: Hudson River Trading, Roblox, TikTok

Array · Binary Indexed Tree · Binary Search · Ordered Set

Concatenation of Array

Given an integer array nums, produce ans by concatenating nums with itself so that ans has length 2n and ans[i]=nums[i], ans[i+n]=nums[i] for 0<=i<n; this is…

Companies: Bloomberg, Google

Array · Simulation

Container With Most Water

Given heights of vertical lines at unit-spaced x-coordinates, pick two indices i<j to maximize the area min(height[i],height[j])*(j-i). With n up to 1e5, the problem requires…

Companies: Amazon, Bloomberg, Cisco, Flipkart +4

Array · Greedy · Two Pointers

Contiguous Array

Find the maximum length of a contiguous subarray in a binary array that contains an equal number of 0s and 1s. This is solved by…

Companies: Cisco

Array · Hash Table · Prefix Sum

Count Non Decreasing Arrays With Given Digit Sums

Companies: Microsoft

Array · Dynamic Programming · Prefix Sum

Count Number of Nice Subarrays

Count the number of contiguous subarrays that contain exactly k odd numbers in an integer array. The core challenge is to do this in linear…

Companies: TikTok

Array · Hash Table · Math · Prefix Sum

Daily Temperatures

For each day in an array of daily temperatures, determine how many days you must wait until a warmer temperature appears (or 0 if none)…

Companies: Anduril, Chime, Goldman Sachs

Array · Monotonic Stack · Stack

Design Circular Queue

Implement a fixed-size circular queue (ring buffer) supporting enqueue, dequeue, Front/Rear, isEmpty and isFull operations without using built-in queue types. The core…

Companies: NVIDIA

Array · Design · Linked List · Queue

Dungeon Game

Given a grid of integers (positive heal, negative damage) and moves only right or down, find the minimum positive initial health so the running health…

Companies: Intuit

Array · Dynamic Programming · Matrix

Encrypt and Decrypt Strings

Implement an Encrypter that maps each character to a two-letter code and supports encrypting by replacing characters and decrypting by counting how many dictionary words…

Companies: Duolingo

Array · Design · Hash Table · String

Find All Lonely Numbers in the Array

Find all integers that occur exactly once in nums and whose immediate neighbors (x-1 and x+1) do not appear in the array; return these "lonely"…

Companies: Apple

Array · Counting · Hash Table

Find the Winner of the Circular Game

Given n people seated in a circle, repeatedly remove every k-th person clockwise until one remains and return their label — the classic Josephus problem…

Companies: Goldman Sachs

Array · Math · Queue · Recursion

Fruit Into Baskets

Given an array of fruit types where you can pick from a contiguous sequence while carrying at most two distinct types (two baskets), return the…

Companies: Adobe, Amazon, Meta, Salesforce

Array · Hash Table · Sliding Window

Heaters

Given positions of houses and heaters on a line, find the minimum uniform radius R such that every house is within distance R of some…

Companies: Anduril

Array · Binary Search · Sorting · Two Pointers

High Five

Given a list of (studentId, score) pairs, compute each student's average of their top five scores and return the results as (studentId, average) sorted by…

Companies: Goldman Sachs

Array · Hash Table · Heap (Priority Queue) · Sorting

Largest Rectangle in Histogram

Find the maximum area of a rectangle formed by contiguous bars in a histogram (given bar heights). The core challenge is determining each bar's maximal…

Companies: Bloomberg, Microsoft

Array · Monotonic Stack · Range Minimum/Maximum Query · Stack

Last Stone Weight

Given an array of stone weights, repeatedly take the two heaviest stones, remove them, and if their weights differ push back the difference; return the…

Companies: Apple, Salesforce

Array · Heap (Priority Queue)

Last Stone Weight II

Split the stones into two groups to minimize the absolute difference of their total weights — equivalent to finding the largest subset sum ≤ total_sum/2…

Companies: Apple

0-1 Knapsack · Array · Dynamic Programming · Knapsack Problem

Longest Increasing Subsequence

Given an array of integers, return the length of the longest strictly increasing subsequence; the core challenge is to compute this efficiently—naive DP is O(n^2)…

Companies: PayPal

Array · Binary Search · Dynamic Programming · Longest Increasing Subsequence