Microsoft internship (on campus) - got the offer

OA: 2 questions in 60 min, one string and one DP on grid.

Round 1: reverse linked list in groups of k. Then discussion on how I'd design an LRU cache (hashmap + doubly linked list), didn't have to write full code.

Round 2: validate BST. I first said inorder traversal, he asked for a different approach, did the min/max range one. Then 15 min on my project.

Round 3: mostly behavioural + find the duplicate number.

What I think helped: talking while coding and writing test cases before they asked.