From various on-site interviews, I was asked:

• Design and implement an iterator for a singly-linked list class.
• How would you design a garbage collector?
• Given two connected singly-linked lists (forming a T-shaped structure), find the node where they connect.
• Implement a complete singly-linked list class in C++.
• Cycle detection in singly-linked lists.
• Describe the differences between C++ and Java.
• Determine if a binary tree is balanced.
• Describe the architecture of the systems of my current employer.
• Describe how to maintain data integrity across concurrent reads/writes to/from a database.
• How to remove duplicates from an array.
• When does it make sense to store a tree ADT in an array?
• How would you organize a data structure used for parsing arithmetic operations? (e.g., 3*2 + 4 = 10)
• Write a Python script to scan files in a directory for a word. Return true if the word is found in at least one file and false otherwise.

Nothing truly unexpected.

Thorough knowledge of OOP, data structures, and algorithms will serve you well.