Introduction

In this blog post, we'll share the most commonly asked coding interview questions at Airbnb. If you don't have months to study for your interviews, you can use AI tools like Chatmagic to generate solutions quickly and efficiently - helping you pass the interviews and get the job offer!

Problem #1: Maximum Profit in Job Scheduling

We have n jobs, where every job is scheduled to be done from startTime[i] to endTime[i], obtaining a profit of profit[i]. You're given the startTime, endTime and profit arrays, return the maximum profit you can take such that there are no two jobs in the subset with overlapping time range. If you choose a job that ends at time X you will be able to start another job that starts at time X. Example 1: Input: startTime = [1,2,3,3], endTime = [3,4,5,6], profit = [50,10,40,70] Output: 120 Explanation: The subset chosen is the first and fourth job. Time range [1-3]+[3-6] , we get profit of 120 = 50 + 70. Example 2: Input: startTime = [1,2,3,4,6], endTime = [3,5,10,6,9], profit = [20,20,100,70,60] Output: 150 Explanation: The subset chosen is the first, fourth and fifth job. Profit obtained 150 = 20 + 70 + 60. Example 3: Input: startTime = [1,1,1], endTime = [2,3,4], profit = [5,6,4] Output: 6 Constraints: 1 <= startTime.length == endTime.length == profit.length <= 5 * 104 1 <= startTime[i] < endTime[i] <= 109 1 <= profit[i] <= 104

Topics: Array, Binary Search, Dynamic Programming, Sorting

Problem #2: Palindrome Pairs

You are given a 0-indexed array of unique strings words. A palindrome pair is a pair of integers (i, j) such that: 0 <= i, j < words.length, i != j, and words[i] + words[j] (the concatenation of the two strings) is a palindrome. Return an array of all the palindrome pairs of words. You must write an algorithm with O(sum of words[i].length) runtime complexity. Example 1: Input: words = ["abcd","dcba","lls","s","sssll"] Output: [[0,1],[1,0],[3,2],[2,4]] Explanation: The palindromes are ["abcddcba","dcbaabcd","slls","llssssll"] Example 2: Input: words = ["bat","tab","cat"] Output: [[0,1],[1,0]] Explanation: The palindromes are ["battab","tabbat"] Example 3: Input: words = ["a",""] Output: [[0,1],[1,0]] Explanation: The palindromes are ["a","a"] Constraints: 1 <= words.length <= 5000 0 <= words[i].length <= 300 words[i] consists of lowercase English letters.

Topics: Array, Hash Table, String, Trie

Problem #3: Simple Bank System

You have been tasked with writing a program for a popular bank that will automate all its incoming transactions (transfer, deposit, and withdraw). The bank has n accounts numbered from 1 to n. The initial balance of each account is stored in a 0-indexed integer array balance, with the (i + 1)th account having an initial balance of balance[i]. Execute all the valid transactions. A transaction is valid if: The given account number(s) are between 1 and n, and The amount of money withdrawn or transferred from is less than or equal to the balance of the account. Implement the Bank class: Bank(long[] balance) Initializes the object with the 0-indexed integer array balance. boolean transfer(int account1, int account2, long money) Transfers money dollars from the account numbered account1 to the account numbered account2. Return true if the transaction was successful, false otherwise. boolean deposit(int account, long money) Deposit money dollars into the account numbered account. Return true if the transaction was successful, false otherwise. boolean withdraw(int account, long money) Withdraw money dollars from the account numbered account. Return true if the transaction was successful, false otherwise. Example 1: Input ["Bank", "withdraw", "transfer", "deposit", "transfer", "withdraw"] [[[10, 100, 20, 50, 30]], [3, 10], [5, 1, 20], [5, 20], [3, 4, 15], [10, 50]] Output [null, true, true, true, false, false] Explanation Bank bank = new Bank([10, 100, 20, 50, 30]); bank.withdraw(3, 10); // return true, account 3 has a balance of $20, so it is valid to withdraw $10. // Account 3 has $20 - $10 = $10. bank.transfer(5, 1, 20); // return true, account 5 has a balance of $30, so it is valid to transfer $20. // Account 5 has $30 - $20 = $10, and account 1 has $10 + $20 = $30. bank.deposit(5, 20); // return true, it is valid to deposit $20 to account 5. // Account 5 has $10 + $20 = $30. bank.transfer(3, 4, 15); // return false, the current balance of account 3 is $10, // so it is invalid to transfer $15 from it. bank.withdraw(10, 50); // return false, it is invalid because account 10 does not exist. Constraints: n == balance.length 1 <= n, account, account1, account2 <= 105 0 <= balance[i], money <= 1012 At most 104 calls will be made to each function transfer, deposit, withdraw.

Topics: Array, Hash Table, Design, Simulation

Problem #4: Text Justification

Given an array of strings words and a width maxWidth, format the text such that each line has exactly maxWidth characters and is fully (left and right) justified. You should pack your words in a greedy approach; that is, pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly maxWidth characters. Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line does not divide evenly between words, the empty slots on the left will be assigned more spaces than the slots on the right. For the last line of text, it should be left-justified, and no extra space is inserted between words. Note: A word is defined as a character sequence consisting of non-space characters only. Each word's length is guaranteed to be greater than 0 and not exceed maxWidth. The input array words contains at least one word. Example 1: Input: words = ["This", "is", "an", "example", "of", "text", "justification."], maxWidth = 16 Output: [ "This is an", "example of text", "justification. " ] Example 2: Input: words = ["What","must","be","acknowledgment","shall","be"], maxWidth = 16 Output: [ "What must be", "acknowledgment ", "shall be " ] Explanation: Note that the last line is "shall be " instead of "shall be", because the last line must be left-justified instead of fully-justified. Note that the second line is also left-justified because it contains only one word. Example 3: Input: words = ["Science","is","what","we","understand","well","enough","to","explain","to","a","computer.","Art","is","everything","else","we","do"], maxWidth = 20 Output: [ "Science is what we", "understand well", "enough to explain to", "a computer. Art is", "everything else we", "do " ] Constraints: 1 <= words.length <= 300 1 <= words[i].length <= 20 words[i] consists of only English letters and symbols. 1 <= maxWidth <= 100 words[i].length <= maxWidth

Topics: Array, String, Simulation

Problem #7: Subarray Product Less Than K

Given an array of integers nums and an integer k, return the number of contiguous subarrays where the product of all the elements in the subarray is strictly less than k. Example 1: Input: nums = [10,5,2,6], k = 100 Output: 8 Explanation: The 8 subarrays that have product less than 100 are: [10], [5], [2], [6], [10, 5], [5, 2], [2, 6], [5, 2, 6] Note that [10, 5, 2] is not included as the product of 100 is not strictly less than k. Example 2: Input: nums = [1,2,3], k = 0 Output: 0 Constraints: 1 <= nums.length <= 3 * 104 1 <= nums[i] <= 1000 0 <= k <= 106

Topics: Array, Binary Search, Sliding Window, Prefix Sum

Problem #9: Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "". The testcases will be generated such that the answer is unique. Example 1: Input: s = "ADOBECODEBANC", t = "ABC" Output: "BANC" Explanation: The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t. Example 2: Input: s = "a", t = "a" Output: "a" Explanation: The entire string s is the minimum window. Example 3: Input: s = "a", t = "aa" Output: "" Explanation: Both 'a's from t must be included in the window. Since the largest window of s only has one 'a', return empty string. Constraints: m == s.length n == t.length 1 <= m, n <= 105 s and t consist of uppercase and lowercase English letters. Follow up: Could you find an algorithm that runs in O(m + n) time?

Topics: Hash Table, String, Sliding Window

Problem #10: Shortest Path in Binary Matrix

Given an n x n binary matrix grid, return the length of the shortest clear path in the matrix. If there is no clear path, return -1. A clear path in a binary matrix is a path from the top-left cell (i.e., (0, 0)) to the bottom-right cell (i.e., (n - 1, n - 1)) such that: All the visited cells of the path are 0. All the adjacent cells of the path are 8-directionally connected (i.e., they are different and they share an edge or a corner). The length of a clear path is the number of visited cells of this path. Example 1: Input: grid = [[0,1],[1,0]] Output: 2 Example 2: Input: grid = [[0,0,0],[1,1,0],[1,1,0]] Output: 4 Example 3: Input: grid = [[1,0,0],[1,1,0],[1,1,0]] Output: -1 Constraints: n == grid.length n == grid[i].length 1 <= n <= 100 grid[i][j] is 0 or 1

Topics: Array, Breadth-First Search, Matrix