Return the average of the values in a given range in a binary search tree. Example: [4,11] => avg(6,10,4,9) => return 7.xx This problem asks you to comp…

Instagram College Students Visiting Search on the Day of Registration, by Country Table: ig_users This table has one row for every Instagram user. Colum…

Find the unique element in an array where all other elements appear twice except one. Examples: [1, 1, 4, 4, 7, 8, 8, 29, 29] -> 7 [1, 2, 2, 3, 3] -&…

Implement a simplified version of a banking system. Plan your design according to the level specifications below: Level 1: The banking system should sup…

This problem is a standard weighted random selection. Build a prefix-sum array based on city populations and map a random value into one of the prefix intervals. This guarantees output probabilities match the weight distribution, and repeated queries remain efficient. The key is prefix sums plus binary search for fast selection. The BST property allows…

The solution uses a stack to simulate function calls. A“begin”event pushes a new frame and pauses the previous function, while an“end”event pops the function and accumulates its exclusive time based on timestamp differences. Properly tracking the previous timestamp is essential to handle nesting correctly. The VOprep team has long accompanied candidates through various major company OAs and…

Standing on the left side gives the leftmost node of each level, but the ordering must be reversed from bottom to top. Standing on the right side gives the rightmost node level by level from top to bottom. The problem is solved with BFS level traversal and extracting the appropriate visible node at each level….

This is the 2D extension of the range counting problem. Build a 2D prefix-sum matrix pre[i][j] for ones in the rectangle from (0,0) to (i,j), then answer any subgrid query in O(1) time using the inclusion–exclusion formula. It tests understanding of 2D prefix sums and careful boundary handling The VOprep team has long accompanied candidates through various…

This problem is a classic range query task. The optimal solution precomputes a 1D prefix-sum array where prefix[i] stores the number of ones up to index , then each query runs in O(1) time using prefix[end] – prefix[start-1]. It tests preprocessing, time–space trade-offs, and clean API design. The VOprep team has long accompanied candidates through various major…

The task is to evaluate an expression with only + and *, respecting operator precedence. Typical solutions use a stack to accumulate intermediate products, or track the current multiplication block during a single pass. The VOprep team has long accompanied candidates through various major company OAs and VOs, including Meta, Amazon, Citadel, SIG, providing real-time voice assistance,…

A classic weighted random selection question: build a prefix-sum array, generate a random number within the weighted range, and use binary search to find the correct index. Commonly tested in Meta interviews for probability distribution and prefix-sum logic The VOprep team has long accompanied candidates through various major company OAs and VOs, including Meta, Amazon, Citadel, SIG,…

This Meta interview question asks for all root-to-leaf path sums in a binary tree. A depth-first search is used to propagate the running sum, recording values when a leaf is reached. It tests recursion, tree traversal, and handling of leaf conditions. The VOprep team has long accompanied candidates through various major company OAs and VOs, including Meta,…

Triplet Card Game — AI Strategy Task You can see there is a 4×4 grid of cards, Ace through Nine.Each turn consists of picking up 3 cards which add up to 15 (Aces count as 1);these cards are then replaced from the deck. If you can’t pick up exactly 3 cards that add up to…

Find the unique element in an array where all elements appear twice except one.Examples: Summary (with approach)Use XOR: since a ^ a = 0, a ^ 0 = a, and XOR is associative/commutative, XOR all numbers; the result is the single number. Runs in O(N) time and O(1) space. Alternative: hash counting in O(N) space….

Imagine an array that contains both integers and nested arrays, such as the following:[8, 4, [5, [9], 3], 6].The depth sum is described as the weighted sum of each integer, weighted by their respective depths. In the example, 8’s depth is 1, while 9’s is 3.Given such an array, calculate its depth sum. Examples Summary…

You are given K sorted integer arrays (non-decreasing). Arrays may contain duplicates within the same array and across different arrays.Return a sorted list of unique integers that appear in any of the arrays (i.e., the set union, sorted). Example:A = [-100, -1, -1, 0, 5]B = [0]C = [-1, 0, 0]Output → [-100, -1, 0,…

Given the root of a binary search tree, return a balanced binary search tree that contains the same node values. If there is more than one valid answer, return any of them.A binary search tree is balanced if the depth of the two subtrees of every node never differs by more than 1. Example:Input: root…

Problem (English original):Given the root of a binary tree containing integers, return a list of all the integers in the tree ordered by column from left to right. Within each column, values should be ordered from top to bottom. Assume a node definition (or language equivalent): Input (example, ASCII tree): Output (example): Summary (approach):BFS/DFS tagging…

Given a string S consisting of lowercase English characters, determine if you can make it a palindrome by removing at most one character. Example: Summary (approach):Use two pointers. On the first mismatch, try skipping either the left or the right character and check if the remaining substring is a palindrome. O(n) time, O(1) space. The VOprep team…

Problem (verbatim):“A multiset (also known as a bag) is a mutable, unordered collection of distinct objects that may appear more than once in the collection. Implement a multiset that implements the following methods:• add(element)• remove(element)• count(for: element)” English summary (concise approach):Back the multiset with a hash map value → frequency. The VOprep team has long accompanied candidates…