Number of Islands

Problem

Count connected groups of 1s in a binary grid, using horizontal and vertical neighbours.

Examples

Example 1

Input: [[1,1,0],[1,0,0],[0,0,1]]

Output: 2

Example 2

Input: [[1,0,1]]

Output: 2

Input and output use JSON-compatible values. For linked-list and tree questions, arrays represent the node structure as described above. Your code should implement solve(input).

Write your solutionImplement solve(input). Your draft is saved in this browser.

Compiler

How to solve Number of Islands

Count connected groups of 1s in a binary grid, using horizontal and vertical neighbours. Flood-fill each unvisited land cell with DFS or BFS. The reference implementation illustrates this approach; check the example and edge cases.

Time and space complexity

O(rows × columns) time and space.

Practise and improve

Choose JavaScript, TypeScript or Python, complete the starter code, then select Run Tests. Request a hint when you need guidance, or choose View solution and confirm if you would like to study the reference implementation.