1. Problem Summary You are given the root of a binary tree.Your task is to return the level order traversal, meaning: Example interpretation: Given tree: Output: 2. Key Insights Level order traversal is essentially a breadth-first traversal We must explore the tree breadth-first rather than depth-first. A queue naturally processes nodes level by level As…

1. Problem Summary You are given an integer array nums. Your task is to determine whether the array can become non-decreasing by modifying at most one element. A non-decreasing array satisfies: Constraints and rules: Example: Example: 2. Key Insights Insight 1: Violations tell the story A violation occurs when: If we encounter more than one…

1. Problem Summary You are given an integer array nums, and your task is to determine whether it is possible to make the array non-decreasing by modifying at most one element. A non-decreasing array satisfies: Rules: Example interpretation:Input: Modify 4 → 2 to get [2,2,3] → return true. Input: Needs at least two modifications →…

1. Problem Summary You are given an integer array nums. Your task is to compute and return a new array result where: This is known as the running sum or prefix sum of the array. Example interpretation:If: Then: 2. Key Insights Running sum accumulates progressively Each position builds on previous sum rather than recomputing from…

1. Problem Summary You are given the head of a singly linked list.Your task is to determine whether the linked list represents a palindrome, meaning: Important details: Example interpretation:Input: Output: Another example: Output: 2. Key Insights Linked lists do not allow reverse indexing Unlike arrays, we cannot compare front and back via indices efficiently. Optimal…

1. Problem Summary You are asked to implement a basic HashMap data structure from scratch without using: Your custom HashMap must support three operations: Behavior requirements: Constraints: 2. Key Insights Direct array is too large Even though key range is bounded (up to 1,000,000), storing a direct array that large is space-inefficient. Hashing required for…

1. Problem Summary You are given an array heights, where each element represents the height of a bar in a histogram.All bars have a width of exactly 1. Your task is to compute the area of the largest rectangle that can be formed within the histogram, where: Example interpretation:If: The largest rectangle has area: So…

1. Problem Summary You are given: Rules: Your task is to compute the minimum number of boats required to rescue everyone. Example interpretation:If: Possible grouping: Total boats: 2. Key Insights 1. Greedy pairing strategy works To minimize boats, we should try pairing the lightest with the heaviest person. 2. Sorting enables two-pointer optimization After sorting:…

1. Problem Summary You are given the head of a sorted singly linked list.Your task is to remove all nodes that have duplicate values, meaning: Return the head of the updated list containing only distinct values. Example interpretation:Input: Values 3 and 4 appear more than once, so remove them entirely. Output: 2. Key Insights Sorted…

1. Problem Summary You are given the heads of two singly linked lists, list1 and list2. Both linked lists are: Your task is to merge the two lists into a single sorted linked list and return the head of the merged list. Important details: Example interpretation:If the lists are: Merged result becomes: 2. Key Insights…