Number of Enclaves

Medium

Given a binary grid where 1 is land and 0 is sea, return the number of land cells from which you cannot walk off the boundary of the grid moving 4-directionally through land.

Example 1

Input:  grid = [[0,0,0,0],[1,0,1,0],[0,1,1,0],[0,0,0,0]]
Output: 3

Example 2

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

Constraints

• 1 <= m, n <= 500
• grid[i][j] is 0 or 1.