Find View By Id: Implement a Custom View Lookup in an Android-Style View Hierarchy
Interview Experience
Problem
In an Android-style view system, each view has an integer ID. Views can be nested in ViewGroups. Implement findViewByIdRecursive that searches the view tree and returns the first view matching the given ID.
java
public abstract class View {
private int id;
public int getId() {
**return** id; }
public View(int id) { this.id = id; }
}
public class ViewGroup extends View {
private List<View> children = new ArrayList<>();
public void addChild(View v) { children.add(v); }
public List<View> getChildren() {
**return** children; }
public ViewGroup(int id) { super(id); }
}
public static View findViewByIdRecursive(View root, int targetId) { ... }
Example:
ViewGroup root(0) -> [View(1), ViewGroup(2) -> [View(3), View(4)]]
findViewByIdRecursive(root, 3) -> View(3)
findViewByIdRecursive(root, 99) -> null
Follow-ups
- DFS or BFS — which is better here, and does it matter for correctness?
- How would you optimize repeated lookups by caching ID-to-view mappings?
- How would you handle the case where duplicate IDs exist in the hierarchy?
- How would you add
findAllViewsByIdthat returns all matching views?
Full Details
Problem
In an Android-style view system, each view has an integer ID. Views can be nested in ViewGroups. Implement findViewByIdRecursive that searches the view tree and returns the first view matching the given ID.
java
public abstract class View {
private int id;
public int getId() {
**return** id; }
public View(int id) { this.id = id; }
}
public class ViewGroup extends View {
private List<View> children = new ArrayList<>();
public void addChild(View v) { children.add(v); }
public List<View> getChildren() {
**return** children; }
public ViewGroup(int id) { super(id); }
}
public static View findViewByIdRecursive(View root, int targetId) { ... }
Example:
ViewGroup root(0) -> [View(1), ViewGroup(2) -> [View(3), View(4)]]
findViewByIdRecursive(root, 3) -> View(3)
findViewByIdRecursive(root, 99) -> null
Follow-ups
- DFS or BFS — which is better here, and does it matter for correctness?
- How would you optimize repeated lookups by caching ID-to-view mappings?
- How would you handle the case where duplicate IDs exist in the hierarchy?
- How would you add
findAllViewsByIdthat returns all matching views?
About This Question
This is a candidate experience report from a nextdoor interview during the phone round.
It covers the following topics: Phone, Graph, Android, System Design, Coding .
Topics
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About Nextdoor Interview Reports
This question was reported by a candidate who interviewed at Nextdoor. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Nextdoor are the higher-signal extractions to take from this report.
For broader preparation context, the Nextdoor interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Nextdoor reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Nextdoor Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Nextdoor reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.