An arithmetic sequence is a list of numbers with a definite pattern. If you take any number in the sequence then subtract it from the previous one, the difference is always a constant. A good arithmetic sequence is an arithmetic sequence with a common difference of either 1 or -1. For example, [4, 5, 6]…

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,…

This problem tests arbitrary-base conversion where the number is stored as a linked list. The core idea is to extract the base-10 value, then repeatedly apply modulo and division to build the new-base list. It evaluates understanding of linked-list big-integer representation and digit extraction logic. The VOprep team has long accompanied candidates through various major company OAs…