Introduction

In this blog post, we'll share the most commonly asked coding interview questions at Verkada. 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: Snapshot Array

Implement a SnapshotArray that supports the following interface: SnapshotArray(int length) initializes an array-like data structure with the given length. Initially, each element equals 0. void set(index, val) sets the element at the given index to be equal to val. int snap() takes a snapshot of the array and returns the snap_id: the total number of times we called snap() minus 1. int get(index, snap_id) returns the value at the given index, at the time we took the snapshot with the given snap_id Example 1: Input: ["SnapshotArray","set","snap","set","get"] [[3],[0,5],[],[0,6],[0,0]] Output: [null,null,0,null,5] Explanation: SnapshotArray snapshotArr = new SnapshotArray(3); // set the length to be 3 snapshotArr.set(0,5); // Set array[0] = 5 snapshotArr.snap(); // Take a snapshot, return snap_id = 0 snapshotArr.set(0,6); snapshotArr.get(0,0); // Get the value of array[0] with snap_id = 0, return 5 Constraints: 1 <= length <= 5 104 0 <= index < length 0 <= val <= 109 0 <= snap_id < (the total number of times we call snap()) At most 5 104 calls will be made to set, snap, and get.

Topics: Array, Hash Table, Binary Search, Design

Problem #2: Basic Calculator II

Given a string s which represents an expression, evaluate this expression and return its value. The integer division should truncate toward zero. You may assume that the given expression is always valid. All intermediate results will be in the range of [-231, 231 - 1]. Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval(). Example 1: Input: s = "3+22" Output: 7 Example 2: Input: s = " 3/2 " Output: 1 Example 3: Input: s = " 3+5 / 2 " Output: 5 Constraints: 1 <= s.length <= 3 105 s consists of integers and operators ('+', '-', '*', '/') separated by some number of spaces. s represents a valid expression. All the integers in the expression are non-negative integers in the range [0, 231 - 1]. The answer is guaranteed to fit in a 32-bit integer.

Topics: Math, String, Stack

Problem #3: Remove Sub-Folders from the Filesystem

Given a list of folders folder, return the folders after removing all sub-folders in those folders. You may return the answer in any order. If a folder[i] is located within another folder[j], it is called a sub-folder of it. A sub-folder of folder[j] must start with folder[j], followed by a "/". For example, "/a/b" is a sub-folder of "/a", but "/b" is not a sub-folder of "/a/b/c". The format of a path is one or more concatenated strings of the form: '/' followed by one or more lowercase English letters. For example, "/leetcode" and "/leetcode/problems" are valid paths while an empty string and "/" are not. Example 1: Input: folder = ["/a","/a/b","/c/d","/c/d/e","/c/f"] Output: ["/a","/c/d","/c/f"] Explanation: Folders "/a/b" is a subfolder of "/a" and "/c/d/e" is inside of folder "/c/d" in our filesystem. Example 2: Input: folder = ["/a","/a/b/c","/a/b/d"] Output: ["/a"] Explanation: Folders "/a/b/c" and "/a/b/d" will be removed because they are subfolders of "/a". Example 3: Input: folder = ["/a/b/c","/a/b/ca","/a/b/d"] Output: ["/a/b/c","/a/b/ca","/a/b/d"] Constraints: 1 <= folder.length <= 4 * 104 2 <= folder[i].length <= 100 folder[i] contains only lowercase letters and '/'. folder[i] always starts with the character '/'. Each folder name is unique.

Topics: Array, String, Depth-First Search, Trie

Problem #4: Transpose Matrix

Given a 2D integer array matrix, return the transpose of matrix. The transpose of a matrix is the matrix flipped over its main diagonal, switching the matrix's row and column indices. Example 1: Input: matrix = [[1,2,3],[4,5,6],[7,8,9]] Output: [[1,4,7],[2,5,8],[3,6,9]] Example 2: Input: matrix = [[1,2,3],[4,5,6]] Output: [[1,4],[2,5],[3,6]] Constraints: m == matrix.length n == matrix[i].length 1 <= m, n <= 1000 1 <= m * n <= 105 -109 <= matrix[i][j] <= 109

Topics: Array, Matrix, Simulation

Problem #5: LRU Cache

Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. Implement the LRUCache class: LRUCache(int capacity) Initialize the LRU cache with positive size capacity. int get(int key) Return the value of the key if the key exists, otherwise return -1. void put(int key, int value) Update the value of the key if the key exists. Otherwise, add the key-value pair to the cache. If the number of keys exceeds the capacity from this operation, evict the least recently used key. The functions get and put must each run in O(1) average time complexity. Example 1: Input ["LRUCache", "put", "put", "get", "put", "get", "put", "get", "get", "get"] [[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]] Output [null, null, null, 1, null, -1, null, -1, 3, 4] Explanation LRUCache lRUCache = new LRUCache(2); lRUCache.put(1, 1); // cache is {1=1} lRUCache.put(2, 2); // cache is {1=1, 2=2} lRUCache.get(1); // return 1 lRUCache.put(3, 3); // LRU key was 2, evicts key 2, cache is {1=1, 3=3} lRUCache.get(2); // returns -1 (not found) lRUCache.put(4, 4); // LRU key was 1, evicts key 1, cache is {4=4, 3=3} lRUCache.get(1); // return -1 (not found) lRUCache.get(3); // return 3 lRUCache.get(4); // return 4 Constraints: 1 <= capacity <= 3000 0 <= key <= 104 0 <= value <= 105 At most 2 * 105 calls will be made to get and put.

Topics: Hash Table, Linked List, Design, Doubly-Linked List

Problem #6: Interval List Intersections

You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of intervals is pairwise disjoint and in sorted order. Return the intersection of these two interval lists. A closed interval [a, b] (with a <= b) denotes the set of real numbers x with a <= x <= b. The intersection of two closed intervals is a set of real numbers that are either empty or represented as a closed interval. For example, the intersection of [1, 3] and [2, 4] is [2, 3]. Example 1: Input: firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]] Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]] Example 2: Input: firstList = [[1,3],[5,9]], secondList = [] Output: [] Constraints: 0 <= firstList.length, secondList.length <= 1000 firstList.length + secondList.length >= 1 0 <= starti < endi <= 109 endi < starti+1 0 <= startj < endj <= 109 endj < startj+1

Topics: Array, Two Pointers, Line Sweep

Problem #7: Diameter of Binary Tree

Given the root of a binary tree, return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them. Example 1: Input: root = [1,2,3,4,5] Output: 3 Explanation: 3 is the length of the path [4,2,1,3] or [5,2,1,3]. Example 2: Input: root = [1,2] Output: 1 Constraints: The number of nodes in the tree is in the range [1, 104]. -100 <= Node.val <= 100

Topics: Tree, Depth-First Search, Binary Tree

Problem #8: Number of 1 Bits

Given a positive integer n, write a function that returns the number of set bits in its binary representation (also known as the Hamming weight). Example 1: Input: n = 11 Output: 3 Explanation: The input binary string 1011 has a total of three set bits. Example 2: Input: n = 128 Output: 1 Explanation: The input binary string 10000000 has a total of one set bit. Example 3: Input: n = 2147483645 Output: 30 Explanation: The input binary string 1111111111111111111111111111101 has a total of thirty set bits. Constraints: 1 <= n <= 231 - 1 Follow up: If this function is called many times, how would you optimize it?

Topics: Divide and Conquer, Bit Manipulation