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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.

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

What role is this question designed for?

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

Count Closed Islands

Last updated: Apr 2, 2026

Quick Overview

This question evaluates a candidate's understanding of grid-based connectivity and the ability to detect enclosed regions, testing skills in graph representation, spatial reasoning, and careful handling of boundary conditions.

Oracle

Jan 20, 2026, 12:00 AM

Data Scientist

Technical Screen

Coding & Algorithms

You are given an m x n binary grid representing terrain after flooding.

0 = land
1 = water

A land region is an island if its land cells are connected 4-directionally: up, down, left, or right. A closed island is an island that does not touch any cell on the outer boundary of the grid.

Return the number of closed islands in the grid.

The expected approach is a classic DFS or BFS traversal on a 2D grid.

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