var detX = []int{1, 0, -1, 0}
var detY = []int{0, 1, 0, -1}

func maxAreaOfIsland(grid [][]int) (area int) {
	H := len(grid)
	if H == 0 {
		return
	}
	W := len(grid[0])
	for y := 0; y < H; y++ {
		for x := 0; x < W; x++ {
			area = maxInt(area, dfs(grid, W, H, x, y))
		}
	}
	return
}

func dfs(grid [][]int, W, H, x, y int) (area int) {
	if x < 0 || W <= x || y < 0 || H <= y || grid[y][x] == 0 {
		return
	}
	area++
	grid[y][x] = 0
	for i := 0; i < 4; i++ {
		nx, ny := x+detX[i], y+detY[i]
		area += dfs(grid, W, H, nx, ny)
	}
	return
}

func maxInt(x, y int) int {
	if x < y {
		return y
	}
	return x
}