O(MxN) time, O(1) space
class Solution:
    def maxAreaOfIsland(self, grid: List[List[int]]) -> int:


        def dfs(r, c):

            if r<0 or r>=rows or c<0 or c>=cols or grid[r][c] == 0:
                return 0

            # mark the current node as visited
            grid[r][c] = 0

            return 1 + dfs(r+1, c) + dfs(r-1, c) + dfs(r, c+1) + dfs(r, c-1)

        rows = len(grid)
        cols = len(grid[0])
        max_area = 0

        for r in range(rows):
            for c in range(cols):
                if grid[r][c] == 1:
                    max_area = max(max_area, dfs(r, c))

        return max_area

O(MxN) time, O(MxN) space
class Solution:
    def maxAreaOfIsland(self, grid: List[List[int]]) -> int:

        def dfs(r, c):
            if (r<0 or r>=n or c<0 or c>=m) or (r, c) in visited or grid[r][c] == 0:
                return 0

            # add to visited
            visited.add((r, c))

            # focus on the recursive formulat, I think you completely messed up the recursive formula
            return 1+ dfs(r+1, c) + dfs(r-1, c) + dfs(r, c+1) + dfs(r, c-1)

        visited = set()
        n = len(grid)
        m = len(grid[0])
        maxArea = 0

        for r in range(n):
            for c in range(m):
                # no need to have checks here as you were having. have checks in the base case only
                area = dfs(r, c)
                maxArea = max(area, maxArea)

        return maxAreaa