Surrounded Islands

You are given a two-dimensional integer matrix matrix containing 1s and 0s. 1 represents land and 0 represents water. An island is a group of 1s that are neighboring whose perimeter is surrounded by water. Return the number of completely surrounded islands.

Constraints

• n, m ≤ 250 where n and m are the number of rows and columns in matrix.

https://binarysearch.com/problems/Surrounded-Islands

Examples

Example 1

Input

• matrix =

[[1,1,0,0,0],
 [0,0,0,0,0],
 [0,1,1,1,0],
 [0,1,0,1,0],
 [0,1,1,1,0],
 [0,0,0,0,0]]

Output

• answer = 1

Explanation

There’s 2 islands but only the middle island is completely surrounded.

Solution