Frage im Vorstellungsgespräch bei Amazon

Write a function to check whether a binary tree was a binary search tree. My first function only handled trees with integer values and he asked me to run through the function with a tree of double/float values. I should have asked clarifying questions before I started coding. Design a library (write out all of the classes, etc...), this was an OO question. Missed a few abstractions, basic structure was alright though.