Amazon Software Development Engineer interview questions

Got in contact through college career fair. Had a 45min on-campus interview 3 weeks later. The interviewer was very friendly, he gave helpful hints on how to solve the coding problems. He walked me through my code and pointed out where needs improvements. Some problems he asked were: Given an integer array, find any integer that occurs more than once. Given a binary tree, test whether it is a BST. Given two random nodes in a tree, not necessarily a BST, find their common parent. They really focus on memory usage and time complexity of your algorithm/data structure.