func maxAreaOfIsland(grid [][]int) int {
    m, n := len(grid), len(grid[0])
    ans := 0

    var dfs func(i, j int) int
    dfs = func(i, j int) int {
        grid[i][j] = 0
        area := 1

        // 继续深度优先搜索上下左右为1的格子
        if i + 1 < m && grid[i + 1][j] == 1 {
            area += dfs(i + 1, j)
        }

        if i - 1 >= 0 && grid[i - 1][j] == 1 {
            area += dfs(i - 1, j)
        }

        if j - 1 >= 0 && grid[i][j - 1] == 1 {
            area += dfs(i, j - 1)
        }

        if j + 1 < n && grid[i][j + 1] == 1 {
            area += dfs(i, j + 1)
        }

        return area
    }

    for i := 0; i < m; i++ {
        for j := 0; j < n; j++ {
            if grid[i][j] == 1 {
                ans = max(ans, dfs(i, j))
            }
        }
    }

    return ans
}