Learnitweb

Author: Editorial Team

  • Merge k Sorted Lists

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    1. Problem Summary You are given an array of k linked lists, where each list is: Your task is to merge all k linked lists into one single sorted linked list and return its head. Example: 2. Key Insights Insight 1: Naive concatenation then sort is inefficient Concatenating and sorting results in: but loses benefits…

  • Insert into a Binary Search Tree

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    1. Problem Summary You are given: Your task is to insert val into the BST while maintaining BST properties and return the updated root. Important points: Example: 2. Key Insights Insight 1: BST insertion follows binary search direction If: Insight 2: Insert when null child encountered When traversal reaches a null position, create new node.…

  • Pairs of Songs With Total Durations Divisible by 60

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    1. Problem Summary You are given an integer array time, where each element represents the duration of a song in seconds. Your task is to determine how many pairs (i, j) exist such that: Important details: Example: 2. Key Insights Insight 1: Modulo remainder drives the condition Instead of checking sums, we examine: Insight 2:…

  • Range Sum of BST

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    1. Problem Summary You are given the root of a Binary Search Tree (BST) and two integers low and high. Your task is to compute the sum of all node values such that: Important details: Example: 2. Key Insights Insight 1: BST ordering allows pruning Because: We can skip entire subtrees: Insight 2: Better than…

  • LeetCode Problem 1306 Jump Game III

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    1. Problem Summary You are given an integer array arr and a starting index start. From index i, you may move to: Your task is to determine whether it is possible to reach any index with value 0. Rules and constraints: Example: 2. Key Insights Insight 1: This is a reachability problem We are exploring…

  • Concatenation of Array

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    1. Problem Summary You are given an integer array nums of length n. Your task is to build a new array ans of length 2n such that: for every index i from 0 to n−1. In other words, you must concatenate the array with itself: Example: 2. Key Insights Insight 1: Output size always exactly…

  • Build Array from Permutation

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    1. Problem Summary You are given an integer array nums of length n, where: You must construct a new array ans such that: and return ans. Example: 2. Key Insights Insight 1: Nested indexing is always valid Since every value in nums is a valid index, accessing nums[nums[i]] is always safe. Insight 2: No reordering…

  • Build Array from Permutation

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    1. Problem Summary You are given an integer array nums where: Your task is to construct a new array ans such that: Then return ans. Example: 2. Key Insights Insight 1: Direct indexing solves it Since nums is a permutation, every index lookup is valid. Insight 2: No need for additional logic No sorting, mapping,…

  • LeetCode Problem 126 Word Ladder II

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    1. Problem Summary You are given: Your task is to: Return all shortest transformation sequences from beginWord to endWord, such that: Example: Input: Output: 2. Key Insights Insight 1: This is a shortest-path problem in word graph Each word is a node.Edges exist between words that differ by exactly one letter. Insight 2: BFS ensures…

  • Binary Tree Pruning

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    1. Problem Summary You are given the root of a binary tree where each node has a value of: Your task is to: Remove (prune) every subtree that does not contain at least one node with value 1. Rules and clarifications: Example: Input: After pruning, output: Another example: Input: After pruning, output: 2. Key Insights…