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5. Longest Palindromic SubstringGiven a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.Example 1:Input: "babad"Output: "bab"Note: "aba" is also a valid answer.Example 2:Input: "cbbd"Outpu

46. PermutationsGiven a collection of distinct integers, return all possible permutations.Example:Input: [1,2,3]Output:[ [1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]]SolutionC++class Solution {public: vector<vector<

84. Largest Rectangle in HistogramGiven n non-negative integers representing the histogram’s bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.Above is a histogram where width of each bar is 1, given height

297. Serialize and Deserialize Binary TreeSerialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be reconstructe

98. Validate Binary Search TreeGiven a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node’s key.The right subtree of a node con

236. Lowest Common Ancestor of a Binary TreeGiven a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the

TitleProblemExample:contentSolutionC++cppPythonpython

22. Generate ParenthesesGiven n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.Example 1:Input: n = 3Output: ["((()))","(()())","(())()","()(())","()()()"]Example 2:Input: n = 1Output: ["()"]Solutio

17. Letter Combinations of a Phone NumberGiven a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.A mapping of digit to letters (just like on the telephon

15. 3SumGiven an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Notice that the solution set must not contain duplicate triplets.Example 1:Input: n

10. Regular Expression MatchingGiven an input string (s) and a pattern §, implement regular expression matching with support for ‘.’ and ‘*’ where:‘.’ Matches any single character.​​​​‘*’ Matches zero or more of the preceding element.The matching shou

206. Reverse Linked ListReverse a singly linked list.Example:Input: 1->2->3->4->5->NULLOutput: 5->4->3->2->1->NULLSolutionC++Sol1:/** * Definition for singly-linked list. * struct ListNode { * int val; * L

105. Construct Binary Tree from Preorder and Inorder TraversalGiven preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.For example, givenpreorder = [3,9,20,15,7]inorder = [

121. Best Time to Buy and Sell StockSay you have an array for which the ith element is the price of a given stock on day i.If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock), design an algorithm

124. Binary Tree Maximum Path SumGiven a non-empty binary tree, find the maximum path sum.For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must conta

104. Maximum Depth of Binary TreeGiven a binary 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.Note: A leaf is a node with no children.Example:Given binary

102. Binary Tree Level Order TraversalGiven a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7re

101. Symmetric TreeGiven a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree [1,2,2,3,4,4,3] is symmetric: 1 / \ 2 2 / \ / \3 4 4 3But the following [1,2,2,null,3,null,3]

215. Kth Largest Element in an ArrayFind the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.Example 1:Input: [3,2,1,5,6,4] and k = 2Output: 5Example 2:Input: [3,2,3

94. Binary Tree Inorder TraversalGiven the root of a binary tree, return the inorder traversal of its nodes’ values.Example:Input: root = [1,null,2,3]Output: [1,3,2]Example 2:Input: root = []Output: []Example 3:Input: root = [1]Output: [1]So

160. Intersection of Two Linked ListsWrite a program to find the node at which the intersection of two singly linked lists begins.For example, the following two linked lists:begin to intersect at node c1.Example 1:Input: intersectVal = 8, listA = [4

240. Search a 2D Matrix IIWrite an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted in ascending from left to right.Integers in each column are sorted in ascending

234. Palindrome Linked ListGiven a singly linked list, determine if it is a palindrome.Example 1:Input: 1->2Output: falseExample 2:Input: 1->2->2->1Output: trueSolutionC++/** * Definition for singly-linked list. * struct ListNode

148. Sort ListGiven the head of a linked list, return the list after sorting it in ascending order.Follow up: Can you sort the linked list in O(n logn) time and O(1) memory (i.e. constant space)?Example 1:Input: head = [4,2,1,3]Output: [1,2,3,4]Exam

155. Min StackDesign a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) – Push element x onto stack.pop() – Removes the element on top of the stack.top() – Get the top element.getMin() – Retrieve the mini

152. Maximum Product SubarrayGiven an integer array nums, find the contiguous subarray within an array (containing at least one number) which has the largest product.Example 1:Input: [2,3,-2,4]Output: 6Explanation: [2,3] has the largest product 6.Ex

141. Linked List CycleGiven head, the head of a linked list, determine if the linked list has a cycle in it.There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following the next pointer. Internal

169. Majority ElementGiven an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.You may assume that the array is non-empty and the majority element always exist in the array.Example 1:I

146. LRU CacheDesign a data structure that follows the constraints of a Least Recently Used (LRU) cache.Implement the LRUCache class:LRUCache(int capacity) Initialize the LRU cache with positive size capacity.int get(int key) Return the value of the k

198. House RobberYou are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and i

139. Word BreakGiven a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words.Note:The same word in the dictionary may be reused

238. Product of Array Except SelfGiven an array nums of n integers where n > 1, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].Example:Input: [1,2,3,4]Output: [24,12,8,6]Constraint:

279. Perfect SquaresGiven a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, …) which sum to n.Example 1:Input: n = 12Output: 3 Explanation: 12 = 4 + 4 + 4.Example 2:Input: n = 13Output: 2Explanation:

207. Course ScheduleThere are a total of numCourses courses you have to take, labeled from 0 to numCourses-1.Some courses may have prerequisites, for example to take course 0 you have to first take course 1, which is expressed as a pair: [0,1]Given the

200. Number of IslandsGiven a 2d grid map of '1’s (land) and '0’s (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are a

79. Word SearchGiven a 2D board and a word, find if the word exists in the grid.The word can be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertically neighboring. The same letter cell may not

128. Longest Consecutive SequenceGiven an unsorted array of integers, find the length of the longest consecutive elements sequence.Your algorithm should run in O(n) complexity.Example:Input: [100, 4, 200, 1, 3, 2]Output: 4Explanation: The longest con

136. Single NumberGiven a non-empty array of integers, every element appears twice except for one. Find that single one.Example 1:Input: [2,2,1]Output: 1Example 2:Input: [4,1,2,1,2]Output: 4SolutionC++class Solution {public: int singleNumb

76. Minimum Window SubstringGiven a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).Example:Input: S = "ADOBECODEBANC", T = "ABC"Output: "BANC"SolutionC++class Solution {public:

75. Sort ColorsGiven an array with n objects colored red, white or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white and blue.Here, we will use the integers 0, 1, and 2 to represent the color