Given an m x n binary matrix grid, return the area of the largest island in grid. If no island exists, return 0.

An island is a group of 1s representing land cells connected 4-directionally: up, down, left, or right. The area of an island is the total number of 1 cells in that connected group.

Assume all four edges of the grid are surrounded by water.

Example 1:

Input: grid = [
  [0,1,0,0,1,0,0,1,0,0,0,1,0],
  [0,0,0,0,1,0,0,1,1,0,0,1,0],
  [0,0,0,0,0,0,0,0,0,0,0,1,1],
  [0,0,0,0,0,0,0,0,0,0,0,0,0],
  [0,1,0,0,0,1,0,1,0,0,1,1,1],
  [0,1,1,0,0,1,1,1,0,0,1,0,0],
  [0,1,1,0,0,0,0,1,0,0,1,1,1],
  [0,0,0,0,0,0,0,0,0,0,0,0,1],
  [0,0,0,0,0,1,1,1,0,0,1,1,1],
  [0,0,0,0,0,0,0,1,1,1,0,0,0]
]
Output: 11  
Explanation: The answer is not 17 because islands are connected only 4-directionally. Diagonal connections do not count.
The extra bottom island has area 6 and is only diagonally connected, so it does not merge with the largest island.

Example 2:

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

Constraints

m == grid.length

n == grid[0].length

1 <= m <= 50

1 <= n <= 50

grid[i][j] is either 0 (water) or 1 (land)

grid is rectangular (every row has the same length n, meaning grid[i].length == n)

72. Area of Largest Island