Find the number of islands

Find the number of islands.

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

This is an variation of the standard problem: “Counting number of connected components in a undirected graph”.

A connected component – connected component of an undirected graph is a subgraph in which every two vertices are connected to each other by a path(s), and which is connected to no other vertices outside the subgraph.

This problem can be solved by DFS

The eight possible moves:

-1, -1

0, -1

1, -1

-1, 0

0 , 0

1, 0

-1, 1

0, 1

1, 1

  1. Set numberOfIsLands = 0
  2. Create visitedVertex boolean array
  3. Iterate rows of graph from 0 to n-1
    1. Iterate cols of graph from 0 to n-1
      1. If graph[row][col] is not visited then
        1. Set numberOfIsLands = numberOfIsLands + 1
        2. Call modified DFS with graph, current row, current column and visitedVertex array
  4. return numberOfIsLands


Connected Components

Latest Source Code:


 Number of Islands are: 5
Author: Hrishikesh Mishra