Implement placeholder-based pattern matcher

Q: Implement placeholder-based pattern matcher

This question evaluates a candidate's ability to implement linear-time string parsing and placeholder substitution with dictionary lookups, including robust error reporting for missing keys.

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Q: What difficulty level is this interview question?

This is a medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Zillow.

Q: What role is this question designed for?

This question is commonly asked for Machine Learning Engineer candidates at Zillow during technical interviews.

Question

You are given:

A string s that may contain placeholders delimited by the % character.
A dictionary dict mapping keys (strings) to replacement values (strings).

A placeholder is any substring that starts and ends with %, for example %key%. The text between the two % characters (here, key) is used as a lookup key in dict.

Example:

s = "a%sd%fasd%dog%sdfisan"
dict = { "sd": "HELLO", "dog": "CAT" }

Expected output:

"aHELLOfasdCATsdfisan"

Rules

Parse s from left to right.
Text outside of %...% is copied directly to the output.
When you encounter a % , you start reading a key until the next % :
- The characters between the two % characters form the key.
- Look up this key in dict .
- If the key exists, append dict[key] to the output.
- If the key does not exist in dict , the function should report an error (for example, by returning a special error value or throwing an exception; define your choice clearly in your solution).
You may assume that % characters are properly paired (no unmatched % ).
There is no escaping mechanism for % (every % starts or ends a placeholder).

Task

Implement a function that performs this substitution according to the rules above.
Clearly specify:
- The function signature in the programming language of your choice.
- How errors are represented/returned when a key is missing from dict .
Aim for a solution that runs in linear time in the length of s (plus the cost of dictionary lookups).

Implement placeholder-based pattern matcher

Quick Overview

Rules

Task

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