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206. Reverse Linked List  Given the head of a singly linked list, reverse the list, and return the reversed list. Example 1: Input: head = [1,2,3,4,5]Output: [5,4,3,2,1]Example 2: Input: head = [1,2]Output: [2,1]Example 3:Input: head = []Output: [] Constraints:The number of nodes in the list is the range [0, 5000].-5000  class Solution: def reverseList(self, head: Optional[ListNode]) -> Optio..

213. House Robber IIYou are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile, adjacent houses have a security system connected, and it will automatically contact the police if two adjacent houses were broken into on..

79. Word Search Given an m x n grid of characters board and a string word, return true if word exists in the grid.The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once. Example 1:Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABC..

카데인 알고리즘카데인 알고리즘이란, Dynamic Programming 을 활용해 시간복잡도 O(N)으로 배열의 최대 부분합을 구해는 알고리즘이다.N번째 원소를 갖는 부분배열의 최댓값을 N-1번째 원소를 갖는 부분배열의 최댓값을 이용해 구하는 방식이다. N-1번째 원소를 갖는 부분배열의 최댓값을 안다고 가정했을 때, N번째 원소를 갖는 부분배열의 최댓값은 아래와 같이 결정될 수 있다. N-1번째 원소를 갖는 부분배열에 포함될 수도 있고, 아니면 원소 하나로 구성된 부분배열이 만들어질 수 있다는 의미와 같다.  코드def kadane_algorithm(arr): prev_max=arr[0] res_max=arr[0] for i in range(1, len(arr)): pre..

39. Combination SumGiven an array of distinct integers candidates and a target integer target, return a list of all unique combinations of candidates where the chosen numbers sum to target. You may return the combinations in any order.The same number may be chosen from candidates an unlimited number of times. Two combinations are unique if the frequency  of at least one of the chosen numbers is ..

121. Best Time to Buy and Sell Stock It's simple to figure out the days to buy and to sell. Just update the maximum profit iterating over the array of prices. 1. Keep track of the day to buy the stock at the lowest price while iterating over the prices.2. Maximize the profilt by determining whether to sell or not. class Solution: def maxProfit(self, prices: List[int]) -> int: profit = ..

128. Longest Consecutive Sequence1. O(N Log(N)) Solution - mineclass Solution: def longestConsecutive(self, nums: List[int]) -> int: heapq.heapify(nums) ans, tmp = 0, [] while nums: num = heapq.heappop(nums) if not tmp: tmp.append(num) else: if tmp[-1] == num: continue elif tm..

[ Problem ]An additive number is a string whose digits can form an additive sequence.A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent number in the sequence must be the sum of the preceding two.Given a string containing only digits, return true if it is an additive number or false otherwise.Note: Numbers in the additive sequence c..

[ Problem ]A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.For example, "0.1.2.201" and "192.168.1.1" are valid IP addresses, but "0.011.255.245", "192.168.1.312" and "192.168@1.1" are invalid IP addresses.Given a string s containing only digits, return all possible valid IP addresses that ..

[ Problem ]You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length at that position.Return true if you can reach the last index, or false otherwise. Example 1:Input: nums = [2,3,1,1,4]Output: trueExplanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.Example 2:Input: nums =..