You are given the root of a binary tree. Your task: Return the sum of all left leaves. Definitions: Example: Another example: Problem Understanding You must walk through the tree and identify leaf nodes, but only those that: Important clarifications: Logic Explained in Simple English The simplest way to think about solving this: Why this…

You must design a data structure that supports: Meaning: Example: Problem Understanding Key observations: Brute force checking becomes far too slow. So we need a smarter way to detect whether the ending of the current stream matches any word. Logic Explained in Simple English The fastest method relies on a key insight: Instead of storing…

You are given a set of non-overlapping axis-aligned rectangles. Each rectangle is represented as: Where: Your task: Design a data structure that supports: The catch: Every integer point covered by the rectangles must have an equal probability of being chosen. Example: Problem Understanding Important characteristics: because both edges are inclusive Goal: Ensure uniform random distribution…

You are given an integer array nums. Your task: Return an array where all even numbers come first, followed by all odd numbers. Important notes: Example: Another example: Problem Understanding Definition reminder: The goal is simply to partition the array so that: Constraints: This is a partitioning problem, not a sorting problem. Logic Explained in…

You are given the head of a singly linked list. Your task is to reorder the list into the following pattern: becomes: You must: Example: Another: Problem Understanding Key observations: So we need a linked-list–friendly strategy. Logic Explained in Simple English To reorder the list, a clean strategy is: Step 1: Split the list into…

You are given a sentence consisting of words separated by spaces. You must transform it into Goat Latin according to these rules: For each word in order: Example: Another example: Problem Understanding Important details: Logic Explained in Simple English Here’s the simplest way to think about this transformation: Why this works: Step-by-Step Approach Java Implementation…

You are given two integers: Your task: Return all non-negative integers of length n such that: Example: Another example: Problem Understanding We must generate numbers with: Important details: This is a number construction problem, not a checking problem. Logic Explained in Simple English A simple way to think about building valid numbers: This naturally suggests…

You are given: Candies must be distributed in this repeating pattern: 1st person gets 1 candy2nd person gets 2 candies3rd person gets 3 candies… and so on When reaching the last person, distribution continues again from the first person, increasing the next giveaway amount each time. If candies run out, give the remaining amount to…

This is a challenging problem involving topological sorting, grouping, and dependency ordering. You are given: If no valid ordering exists, return an empty list. Example: Problem Understanding Key details: So ordering constraints exist at two levels: 1. Between groups If any item in group A depends on an item in group B,then group B must…

You are given an array where each element represents the price of a stock on a given day. Your task: Find the maximum profit achievable with at most TWO buy-and-sell transactions. Rules: Example: Problem Understanding This is an extension of earlier stock problems: Problem Allowed Transactions 121 1 transaction 122 unlimited 123 at most 2…