Introduction

In this blog post, we'll share the most commonly asked coding interview questions at MongoDB. 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: 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 #2: Merge k Sorted Lists

You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. Example 1: Input: lists = [[1,4,5],[1,3,4],[2,6]] Output: [1,1,2,3,4,4,5,6] Explanation: The linked-lists are: [ 1->4->5, 1->3->4, 2->6 ] merging them into one sorted list: 1->1->2->3->4->4->5->6 Example 2: Input: lists = [] Output: [] Example 3: Input: lists = [[]] Output: [] Constraints: k == lists.length 0 <= k <= 104 0 <= lists[i].length <= 500 -104 <= lists[i][j] <= 104 lists[i] is sorted in ascending order. The sum of lists[i].length will not exceed 104.

Topics: Linked List, Divide and Conquer, Heap (Priority Queue), Merge Sort

Problem #3: Insert Interval

You are given an array of non-overlapping intervals intervals where intervals[i] = [starti, endi] represent the start and the end of the ith interval and intervals is sorted in ascending order by starti. You are also given an interval newInterval = [start, end] that represents the start and end of another interval. Insert newInterval into intervals such that intervals is still sorted in ascending order by starti and intervals still does not have any overlapping intervals (merge overlapping intervals if necessary). Return intervals after the insertion. Note that you don't need to modify intervals in-place. You can make a new array and return it. Example 1: Input: intervals = [[1,3],[6,9]], newInterval = [2,5] Output: [[1,5],[6,9]] Example 2: Input: intervals = [[1,2],[3,5],[6,7],[8,10],[12,16]], newInterval = [4,8] Output: [[1,2],[3,10],[12,16]] Explanation: Because the new interval [4,8] overlaps with [3,5],[6,7],[8,10]. Constraints: 0 <= intervals.length <= 104 intervals[i].length == 2 0 <= starti <= endi <= 105 intervals is sorted by starti in ascending order. newInterval.length == 2 0 <= start <= end <= 105

Topics: Array

Problem #4: Merge Two Binary Trees

You are given two binary trees root1 and root2. Imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not. You need to merge the two trees into a new binary tree. The merge rule is that if two nodes overlap, then sum node values up as the new value of the merged node. Otherwise, the NOT null node will be used as the node of the new tree. Return the merged tree. Note: The merging process must start from the root nodes of both trees. Example 1: Input: root1 = [1,3,2,5], root2 = [2,1,3,null,4,null,7] Output: [3,4,5,5,4,null,7] Example 2: Input: root1 = [1], root2 = [1,2] Output: [2,2] Constraints: The number of nodes in both trees is in the range [0, 2000]. -104 <= Node.val <= 104

Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree

Problem #5: Stock Price Fluctuation

You are given a stream of records about a particular stock. Each record contains a timestamp and the corresponding price of the stock at that timestamp. Unfortunately due to the volatile nature of the stock market, the records do not come in order. Even worse, some records may be incorrect. Another record with the same timestamp may appear later in the stream correcting the price of the previous wrong record. Design an algorithm that: Updates the price of the stock at a particular timestamp, correcting the price from any previous records at the timestamp. Finds the latest price of the stock based on the current records. The latest price is the price at the latest timestamp recorded. Finds the maximum price the stock has been based on the current records. Finds the minimum price the stock has been based on the current records. Implement the StockPrice class: StockPrice() Initializes the object with no price records. void update(int timestamp, int price) Updates the price of the stock at the given timestamp. int current() Returns the latest price of the stock. int maximum() Returns the maximum price of the stock. int minimum() Returns the minimum price of the stock. Example 1: Input ["StockPrice", "update", "update", "current", "maximum", "update", "maximum", "update", "minimum"] [[], [1, 10], [2, 5], [], [], [1, 3], [], [4, 2], []] Output [null, null, null, 5, 10, null, 5, null, 2] Explanation StockPrice stockPrice = new StockPrice(); stockPrice.update(1, 10); // Timestamps are [1] with corresponding prices [10]. stockPrice.update(2, 5); // Timestamps are [1,2] with corresponding prices [10,5]. stockPrice.current(); // return 5, the latest timestamp is 2 with the price being 5. stockPrice.maximum(); // return 10, the maximum price is 10 at timestamp 1. stockPrice.update(1, 3); // The previous timestamp 1 had the wrong price, so it is updated to 3. // Timestamps are [1,2] with corresponding prices [3,5]. stockPrice.maximum(); // return 5, the maximum price is 5 after the correction. stockPrice.update(4, 2); // Timestamps are [1,2,4] with corresponding prices [3,5,2]. stockPrice.minimum(); // return 2, the minimum price is 2 at timestamp 4. Constraints: 1 <= timestamp, price <= 109 At most 105 calls will be made in total to update, current, maximum, and minimum. current, maximum, and minimum will be called only after update has been called at least once.

Topics: Hash Table, Design, Heap (Priority Queue), Data Stream, Ordered Set