Software Engineer · Onsite · Coding

Google — Software Engineer ❌ Failed

Level: Unknown Level

Round: Onsite · Type: Coding · Difficulty: 6/10 · Duration: 120 min · Interviewer: Unfriendly

Topics: String Matching, Rule Engine, Wildcard Matching, Prefix Matching

Location: Mountain View, CA

Interview date: 2026-01-16

Got offer: False

Summary

Round 1: Coding

Question: The first question was a simple IP prefix problem, similar to a question discussed online.

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Round 2: Coding

Question: The follow-up question involved designing a rule engine to map binary signals to configuration values based on a pattern list.

Details

Round 1: IP Prefix Matching

The initial question was straightforward, focusing on IP prefix matching.

Round 2: Rule Engine Design

I was asked to design a rule engine that maps binary signals to configuration values. Here's a breakdown:

Problem Description:

The system takes binary signals as input and maps them to specific configuration values. It maintains a list of patterns, each associated with a value.

Input:

• Configuration Phase (Pre-process): A list of key-value pairs is given.
  • Key (Pattern): A string consisting of '0', '1', and '*'.
  • Value: An integer or label (representing a classification ID, weight, or specific action).
• Query Phase: A binary string input (containing only '0' and '1') is provided.

Symbol Definitions:

• '0': Exact match of the character 0.
• '1': Exact match of the character 1.
• '*': Wildcard representing a binary sequence of any length (including an empty sequence).
• '.': Matches any single character

Core Objective:

Implement a match(input) function to find the longest pattern in the pattern list that matches the input and return its value.

Example:

Consider the following pattern list (with \