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

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

Count connected delivery zones

Last updated: Mar 29, 2026

Quick Overview

This question evaluates graph traversal and connected-components detection on grids, measuring competence in grid-based algorithms, neighbor connectivity, and algorithmic analysis of time and space complexity.

Uber

Sep 6, 2025, 12:00 AM

Machine Learning Engineer

Onsite

Coding & Algorithms

Given an m x n grid representing a service area, each cell is either 'Z' (deliverable zone) or '#' (blocked). Two 'Z' cells belong to the same zone if they are 4-directionally adjacent. Implement countZones(grid: List[List[char]]) -> int that returns the number of connected zones. Follow-up: return the sizes of all zones in descending order. Analyze time and space complexity, and then optimize for minimal extra space.

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