Amazon Software Development Engineer interview questions

1. Given a number (not necessarily of type int), find if it is 2^n. What is the complexity? 2. Given a set of points represented by x and y coordinates, find out the first k points that are closest to the origin. What is the complexity? 3. Given an array of integers, return the largest occurrence element times its array index. Do it in place. What is the complexity? 4. Given a binary tree(not necessarily BST), return the sum of all kth level nodes. What is the complexity?