Given a non-empty array of integers where every element appears twice except for one element that appears once, find the single element that appears only once. The solution must have linear time complexity and use only constant space.
Given the head of a linked list, determine if there is a cycle. A cycle occurs if a node can be revisited by following the ’next’ pointers. The ‘pos’ parameter denotes where the last node connects to. If ‘pos’ is -1, there is no cycle.
You are given the root of a binary tree. The task is to return the preorder traversal of the tree. Preorder traversal means visiting the root node first, followed by the left subtree, and then the right subtree.
Given an array nums of size n, return the majority element. The majority element is the element that appears more than n // 2 times. You may assume that the majority element always exists in the array.
