You are given an?m x n?binary matrix?grid, where?0?represents a sea cell and?1?represents a land cell.

A?move?consists of walking from one land cell to another adjacent (4-directionally) land cell or walking off the boundary of the?grid.

Return?the number of land cells in?grid?for which we cannot walk off the boundary of the grid in any number of?moves.

?

Example 1:

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

Output: 3

Explanation: There are three 1s that are enclosed by 0s, and one 1 that is not enclosed because its on the boundary.

Example 2:

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

Output: 0

Explanation: All 1s are either on the boundary or can reach the boundary.

?

Constraints:

• m == grid.length

• n == grid[i].length

• 1 <= m, n <= 500

• grid[i][j]?is either?0?or?1.

Accepted

95,195

Submissions

145,440

DFS 一定要有返回的條件，不然直接就內(nèi)存溢出了。。。

相當(dāng)于把邊上為1的數(shù)字直接改成0，當(dāng)然包含跟他相鄰的數(shù)字，

然后再計算剩下1的數(shù)量，返回即可。

Runtime:?9 ms, faster than?76.21%?of?Java?online submissions for?Number of Enclaves.

Memory Usage:?53.8 MB, less than?76.65%?of?Java?online submissions for?Number of Enclaves.