题目：

题解：

type pair struct{ x, y int }
var dir4 = []pair{{-1, 0}, {1, 0}, {0, -1}, {0, 1}}

func islandPerimeter(grid [][]int) (ans int) {
    n, m := len(grid), len(grid[0])
    for i, row := range grid {
        for j, v := range row {
            if v == 1 {
                for _, d := range dir4 {
                    if x, y := i+d.x, j+d.y; x < 0 || x >= n || y < 0 || y >= m || grid[x][y] == 0 {
                        ans++
                    }
                }
            }
        }
    }
    return
}