Max Area of Island

def maxAreaOfIsland(grid):
    ROWS, COLS = len(grid), len(grid[0])
    visit = set()
    
    def dfs(r, c):
        if (r < 0 or r == ROWS or c < 0 or c == COLS or
            grid[r][c] == 0 or (r, c) in visit):
            return 0
        visit.add((r, c))
        return (1 + dfs(r + 1, c) + dfs(r - 1, c) +
                    dfs(r, c + 1) + dfs(r, c - 1))
                    
    area = 0
    for r in range(ROWS):
        for c in range(COLS):
            area = max(area, dfs(r, c))
    return area