Description: Given the head of a linked list, remove the nth node from the end of the list and return its head. # Definition for singly-linked list. # class ListNode: # def __init__(self, val=0, next=None): # self.val = val # self.next = next ''' [1] two pass) idea:: 1. get the length of linked list, let it len 2. delete len-n+1 th node code:: def removeNthFromEnd(self, head: Optional[ListNode],..

Description: Given a positive integer num, write a function which returns True if num is a perfect square else False. Follow up: Do not use any built-in library function such as sqrt. ''' [1] brute force) code:: def isPerfectSqurare(num): for i in range(1,num): if i*i==num: return True elif i*i>num: # optimization break return False -T/C: O(n) -S/C: O(1) ''' ''' [2] brute force - optimization) c..

Description: Given the head of a linked list and an integer val, remove all the nodes of the linked list that has Node.val == val, and return the new head. # Definition for singly-linked list. # class ListNode: # def __init__(self, val=0, next=None): # self.val = val # self.next = next ''' [1] two pointers - inplace) idea:: this problem can be solved using out-place. but, in-place also can be so..

Description: Given an array of integers nums, you start with an initial positive value startValue. In each iteration, you calculate the step by step sum of startValue plus elements in nums (from left to right). Return the minimum positive value of startValue such that the step by step sum is never less than 1. ''' [1] prefix sum) code:: def minStartValue(self, nums: List[int]) -> int: prefix=cop..

Description: You are given an array of k linked-lists lists, each linked-list is sorted in ascending order. Merge all the linked-lists into one sorted linked-list and return it. # Definition for singly-linked list. # class ListNode: # def __init__(self, val=0, next=None): # self.val = val # self.next = next ''' [1] sort) idea:: 1. while traversing all linked list, append val to list 2. sort it 3..

Description: You are given an integer array prices where prices[i] is the price of a given stock on the ith day. On each day, you may decide to buy and/or sell the stock. You can only hold at most one share of the stock at any time. However, you can buy it then immediately sell it on the same day. Find and return the maximum profit you can achieve. ''' [1] brute force - recursive and calculate a..