Number of Closed Islands

Medium

Given a grid where 0 is land and 1 is water, an island is a maximal group of 4-directionally connected land cells. Return the number of closed islands — islands that are entirely surrounded by water (no land cell touches the grid border).

Example 1

Input:  grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]]
Output: 2

Example 2

Input:  grid = [[1,1,1],[1,0,1],[1,1,1]]
Output: 1

Constraints

• 1 <= m, n <= 100
• grid[i][j] is 0 or 1.