Find islands count in binary 2D matrix

Given a boolean 2D matrix, count the number of islands.

A group of connected 1s forms is an island. Diagonal connections are not counted.

For example:

1 0 1
1 0 0
1 1 1

The above matrix contains 2 islands.

1 0 1
0 1 0
1 0 1

The above matrix contains 4 islands.

Approach

• Initialize result (islands count) as 0
• Iterate through each cell of the 2D matrix.
• Increment result if the cell value is 1 and mark cell with value of 2 and recursively check cell neighbours up/down/left/right. If a neighbour is also equal to 1, mark it as well.

How to use

const findIslandsCount = require('./')

const matrix = [
	[ 0, 1, 0 ],
	[ 0, 0, 1 ],
	[ 0, 1, 0 ]
]
console.log('The result is:', findIslandsCount(matrix)) // The result is 3

How to run test

node index.test.js

Sample test output

$node index.test.js
TESTING PREDEFINED DATA
---------------
index: 0,
matrix:
[
         [ 0, 0, 0 ] ,
         [ 0, 0, 0 ] ,
         [ 0, 0, 0 ] ,
],
count: 0,
expected: 0,
passed: true
---------------
index: 1,
matrix:
[
         [ 1, 1, 1 ] ,
         [ 1, 1, 1 ] ,
         [ 1, 1, 1 ] ,
],
count: 1,
expected: 1,
passed: true
---------------
index: 2,
matrix:
[
         [ 0, 1, 0 ] ,
         [ 1, 0, 1 ] ,
         [ 0, 1, 0 ] ,
],
count: 4,
expected: 4,
passed: true
---------------
index: 3,
matrix:
[
         [ 0, 1, 0 ] ,
         [ 0, 0, 1 ] ,
         [ 0, 1, 0 ] ,
],
count: 3,
expected: 3,
passed: true
---------------
index: 4,
matrix:
[
         [ 0, 1, 0 ] ,
         [ 1, 0, 0 ] ,
         [ 0, 0, 0 ] ,
],
count: 2,
expected: 2,
passed: true
---------------
index: 5,
matrix:
[
         [ 0, 1, 0 ] ,
         [ 1, 1, 1 ] ,
         [ 0, 1, 0 ] ,
],
count: 1,
expected: 1,
passed: true
---------------
index: 6,
matrix:
[
         [ 1, 0, 1 ] ,
         [ 1, 1, 0 ] ,
         [ 0, 0, 1 ] ,
],
count: 3,
expected: 3,
passed: true
---------------
index: 7,
matrix:
[
         [ 1, 0, 1 ] ,
         [ 0, 0, 0 ] ,
         [ 1, 0, 0 ] ,
],
count: 3,
expected: 3,
passed: true
---------------
index: 8,
matrix:
[
         [ 0, 1, 1 ] ,
         [ 0, 1, 1 ] ,
         [ 1, 0, 1 ] ,
],
count: 2,
expected: 2,
passed: true
---------------
index: 9,
matrix:
[
         [ 1, 1, 1 ] ,
         [ 1, 0, 0 ] ,
         [ 1, 1, 0 ] ,
],
count: 1,
expected: 1,
passed: true

PASSED: 10
FAILED: 0


Test 5 random matrix (please check manually):
---
matrix:
[
         [ 1, 0, 1 ] ,
         [ 1, 0, 0 ] ,
         [ 0, 1, 0 ] ,
],
count: 3
---
matrix:
[
         [ 0, 1, 0 ] ,
         [ 1, 1, 1 ] ,
         [ 1, 1, 0 ] ,
],
count: 1
---
matrix:
[
         [ 0, 1, 1 ] ,
         [ 1, 0, 0 ] ,
         [ 0, 1, 1 ] ,
],
count: 3
---
matrix:
[
         [ 1, 0, 1 ] ,
         [ 1, 1, 0 ] ,
         [ 0, 0, 1 ] ,
],
count: 3
---
matrix:
[
         [ 1, 0, 1 ] ,
         [ 1, 1, 0 ] ,
         [ 0, 1, 1 ] ,
],
count: 2

Credits

• Finding Islands In a Binary Matrix (Java)
• Supported JSDoc directives in VSCode
• Principles of Writing Consistent, Idiomatic JavaScript

License

MIT © Sergio Gromov