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This is a easy difficulty Coding & Algorithms question, commonly asked during Onsite rounds at Waymo.

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This question is commonly asked for Data Scientist candidates at Waymo during technical interviews.

Implement nested template string substitution

Last updated: Mar 29, 2026

Quick Overview

This question evaluates understanding of string processing, dependency resolution, recursive expansion, cycle detection, and efficiency techniques such as memoization for nested template substitution.

Waymo

Jan 17, 2026, 12:00 AM

Data Scientist

Onsite

Coding & Algorithms

You are given a dictionary (map) from keys to string templates. Templates may reference other keys using placeholders of the form %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%"), output the fully substituted string.

For the example above:

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

Requirements / edge cases

Placeholders can be nested (a key can reference other keys).
Multiple occurrences of the same placeholder may appear.
Define how you handle:
- Missing keys (e.g., %W% not in dictionary)
- Cycles (e.g., A -> "%B%" , B -> "%A%" )
Aim for efficient time complexity (avoid repeatedly expanding the same key).

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