Microsoft

The interviewer asked me to decode a raw numeric string into alphabetical messages where '1' maps to 'A' through '26' to 'Z'; I started with a linear dynamic programming approach tracking valid one-digit and two-digit splits, but they introduced a follow-up allowing wildcard '*' characters representing any digit from 1 to 9, prompting me to expand the transition states to handle modular arithmetic and edge cases around zero. I was presented with an array of positive integers and asked to find the smallest missing positive integer in O(N) time and O(1) auxiliary space; I initially discussed why sorting or hash sets would violate the memory constraint, then walked through an in-place cycle sort algorithm using the array indices as hash buckets to place each number x at index x - 1. The interviewer framed a problem around a content-recommendation engine where user video watches are logged as directed transitions, asking me to detect all groups of users trapped in isolated consumption loops; I modeled the system as a directed graph and implemented Tarjan’s Strongly Connected Components algorithm using low-link values and a call stack to identify every closed cycle in linear time.