摘要： Given a linked list, reverse the nodes of a linked list k at a time and return its modified list. k is a positive integer and is less than or equal to 阅读全文

摘要： Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. An input string is valid if: No 阅读全文

摘要： Given a linked list, remove the n-th node from the end of list and return its head. Example: Given linked list: 1->2->3->4->5, and n = 2. After removi 阅读全文

摘要： Given an array nums of n integers and an integer target, are there elements a, b, c, and d in nums such that a + b + c+ d = target? Find all unique qu 阅读全文