func islandPerimeter(grid [][]int) (cnt int) {
	m := len(grid)
	if m == 0 {
		return
	}
	n := len(grid[0])
	if n == 0 {
		return
	}
	for i := 0; i < m; i++ {
		for j := 0; j < n; j++ {
			if grid[i][j] == 1 {
				if i == 0 || grid[i-1][j] == 0 {
					cnt++
				}
				if i == m-1 || grid[i+1][j] == 0 {
					cnt++
				}
				if j == 0 || grid[i][j-1] == 0 {
					cnt++
				}
				if j == n-1 || grid[i][j+1] == 0 {
					cnt++
				}
			}
		}
	}
	return
}