Count Islands

You are given a two-dimensional integer array matrix of 0s and 1s.

• 1 represents land.
• 0 represents water.

An island is a maximal group of 1 cells connected horizontally or vertically. Note that neighbors can only be directly horizontal or vertical, not diagonal.

Return the number of islands in matrix.

Examples

Example 1

Input: matrix = [[1,1,0,0,0],[1,1,0,0,1],[0,0,0,1,1],[0,0,0,0,0]]
Output: 2
Explanation: The four 1s in the top-left corner form one island. The 1 at row 1, column 4 connects
down to the two 1s in row 2, forming a second island. No 1 in one island is 4-directionally
adjacent to a 1 in the other.

Example 2

Input: matrix = [[1,0],[0,1]]
Output: 2
Explanation: The two 1s only touch at a corner, which does not count as connected, so they form
two separate islands of size 1 each.

Example 3

Input: matrix = [[0,0,0],[0,0,0]]
Output: 0
Explanation: There is no land at all, so there are no islands.