How do you expand nested placeholders in strings?

Q: How do you expand nested placeholders in strings?

This intermediate-level Coding & Algorithms problem for Data Scientist roles evaluates string parsing and manipulation skills along with dependency resolution techniques such as recursion or graph traversal, cycle detection, and memoization.

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Coding & Algorithms questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master coding & algorithms interviews.

Question

You are given a dictionary of string templates. Keys are identifiers like X, Y, Z. A template may contain placeholders of the form %KEY%, which should be replaced by the fully-expanded value of KEY.

Example dictionary:

X -> "a"
Y -> "b"
Z -> "%X% and %Y%"

Given an input string that may also contain placeholders (e.g., "%X% and %Z%"), return the fully expanded string.

Example:

Input: "%X% and %Z%"
Output: "a and a and b"

Assumptions/requirements to clarify in your solution:

Templates can reference other templates (nested expansion).
Decide how to handle missing keys and cyclic references (e.g., A -> "%B%" , B -> "%A%" ).
Provide time/space complexity for your approach.

How do you expand nested placeholders in strings?

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