Given a linked list, swap every two adjacent nodes and return its head.
You are climbing a stair case. It takes n steps to reach to the top.
Given two binary strings, return their sum (also a binary string).
Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.
Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
Given a string containing just the characters
']', determine if the input string is valid.
Given a linked list, remove the nth node from the end of list and return its head.
Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.
Given a digit string, return all possible letter combinations that the number could represent.