这题飞机上写的。边界条件蛮多的，以为会错但竟然一次AC了。
如果我不知道这是一道easy题，应该就想不出来了。。

    public int islandPerimeter(int[][] grid) {
        int res = 0;
        for (int row = 0; row < grid.length; row++)
            for (int col = 0; col < grid[0].length; col++) {
                if (grid[row][col] == 1) {
                    res += calc(row, col, grid);
                }
            }
        return res;
    }

    private int calc(int row, int col, int[][] matrix) {
        int count = 0;
        if (row == 0 || row > 0 && matrix[row - 1][col] == 0) {
            count++;
        }
        if (col == 0 || col > 0 && matrix[row][col - 1] == 0) {
            count++;
        }
        if (row == matrix.length - 1 || row < matrix.length - 1 && matrix[row + 1][col] == 0) {
            count++;
        }
        if (col == matrix[0].length - 1 || col < matrix[0].length - 1 && matrix[row][col + 1] == 0) {
            count++;
        }
        return count;
    }

另外看到一种计算right neighbor 和 down neighhor最后统一处理的方法:
https://discuss.leetcode.com/topic/68786/clear-and-easy-java-solution