Leetcode Solutions

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  [Solved] You are given the root of a binary search tree (BST) and an integer val. Find the node in the BST that the node’s value equals val and return the subtree rooted with that node. If such a node does not exist, return null.

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  [Solved] You are keeping the scores for a baseball game with strange rules. At the beginning of the game, you start with an empty record. You are given a list of strings operations, where operations[i] is the ith operation you must apply to the record and is one of the following:

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  [Solved] There is a robot starting at the position (0, 0), the origin, on a 2D plane. Given a sequence of its moves, judge if this robot ends up at (0, 0) after it completes its moves.

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  [Solved] You are given an integer array nums with no duplicates. A maximum binary tree can be built recursively from nums using the following algorithm: Create a root node whose value is the maximum value in nums.

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  [Solved] Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.

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  [Solved] Given the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted.

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  [Solved] Write an SQL query to swap all ‘f’ and ‘m’ values (i.e., change all ‘f’ values to ‘m’ and vice versa) with a single update statement and no intermediate temporary tables.

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  [Solved] Write an SQL query to report the movies with an odd-numbered ID and a description that is not “boring”.

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  [Solved] Given the root of an n-ary tree, return the postorder traversal of its nodes’ values. Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

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  [Solved] A country is big if: it has an area of at least three million (i.e., 3000000 km2), or it has a population of at least twenty-five million (i.e., 25000000). Write an SQL query to report the name, population, and area of the big countries.

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  [Solved] Given the root of an n-ary tree, return the preorder traversal of its nodes’ values. Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

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  [Solved] In MATLAB, there is a handy function called reshape which can reshape an m x n matrix into a new one with a different size r x c keeping its original data. You are given an m x n matrix mat and two integers r and c representing the number of rows and the number of columns of the wanted reshaped matrix.

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  [Solved] Given an integer array nums of 2n integers, group these integers into n pairs (a1, b1), (a2, b2), …, (an, bn) such that the sum of min(ai, bi) for all i is maximized. Return the maximized sum.

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  [Solved] Given a n-ary tree, find its maximum depth. The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

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  [Solved] Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

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  [Solved] We define the usage of capitals in a word to be right when one of the following cases holds: All letters in this word are capitals, like “USA”. All letters in this word are not capitals, like “leetcode”. Only the first letter in this word is capital, like “Google”.

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  [Solved] Given a string s, find the longest palindromic subsequence’s length in s. A subsequence is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements.

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  [Solved] Given the root of a binary tree, return an array of the largest value in each row of the tree (0-indexed).

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  [Solved] The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,

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  [Solved] Given the root of a binary search tree (BST) with duplicates, return all the mode(s) (i.e., the most frequently occurred element) in it. If the tree has more than one mode, return them in any order.