Amazon Software Developer Intern interview questions

I got a call from the recruiter about two screen interviews. They asked only coding questions, no behavioral questions at all. Time is not a big problem. There were two recruiters. Each of them asked two questions.

Applied through their careers site. After 2 weeks got a email from HR to schedule two back to back phone interviews. Phone Interview 1- Q1)How will you find if two elements exist in an array which add up to k. Discussed the various approaches. He asked me to implement the HashMap approach on ColabEdit. Q2) Define BST. Describe different approaches to determine whether a tree is BST. Q3) How will you convert a string to Integer. Phone Interview 2- Q1) Write an algo to merge two ascending sorted LL in a descending manner. Gave a recursive solution. Asked me to write a iterative version too. Q2) Asked to give an overview of various sorting algorithms.