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

Explanation:

• The grid contains four islands of 0s.
• The island spanning rows 1 to 3 and columns 1 to 4 is surrounded entirely by 1s. It also encloses the water cell at row 2, column 2. It is therefore closed.
• The single 0 at row 3, column 6 has 1s on all four sides, so it is also closed.
• The two remaining islands both lie in column 7, which is on the border of the grid, so neither of them is closed.
• Two islands are closed, shown in gray, so the answer is 2.

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

Output: 1

Explanation:

• The grid contains three islands of 0s.
• The single 0 at row 1, column 2 has 1s above it, below it, to its left and to its right, so it is closed. It is shown in gray.
• The island formed by rows 0 to 2 of column 0 together with row 0, column 1 lies on the border, so it is not closed.
• The island formed by rows 0 to 2 of column 4 together with row 0, column 3 also lies on the border, so it is not closed.
• One island is closed, so the answer is 1.

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

Output: 2

Explanation:

• The grid contains two islands of 0s, one nested inside the other.
• The outer island is the ring of 0s occupying rows 1 to 5 and columns 1 to 5. It is enclosed by the outer border of 1s, so it is closed.
• The inner island is the single 0 at row 3, column 3. It is enclosed by the inner ring of 1s, so it is also closed.
• Both islands are closed, so the answer is 2.