LeetCode-Island Perimeter

Description：
You are given a map in form of a two-dimensional integer grid where 1 represents land and 0 represents water. Grid cells are connected horizontally/vertically (not diagonally). The grid is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells). The island doesn’t have “lakes” (water inside that isn’t connected to the water around the island). One cell is a square with side length 1. The grid is rectangular, width and height don’t exceed 100. Determine the perimeter of the island.

Example:

[[0,1,0,0],
 [1,1,1,0],
 [0,1,0,0],
 [1,1,0,0]]

Answer: 16

Explanation: The perimeter is the 16 yellow stripes in the image below:

题意：在一个网格中，用1代表一个岛屿，用0代表海水，现在要求计算所有的岛屿的周长；

解法：对于每个岛屿来说，其周长为4，每相邻另外一个岛屿其周长减1，因此，我们遍历整个网格中所有的岛屿，在其初始周长4的前提下，减去相邻的岛屿数，最后对有的的岛屿的周长累加得到结果；

Java

class Solution {
    public int islandPerimeter(int[][] grid) {
        int result = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[i].length; j++) {
                if (grid[i][j] == 1) {
                    result += 4 - aroundCell(grid, i, j);
                }
            }
        }
        return result;
    }
    
    private int aroundCell(int[][] grid, int row, int col) {
        int cnt = 0;
        if (row - 1 >= 0 && grid[row - 1][col] == 1) cnt++;
        if (col - 1 >= 0 && grid[row][col - 1] == 1) cnt++;
        if (row + 1 < grid.length && grid[row + 1][col] == 1) cnt++;
        if (col + 1 < grid[row].length && grid[row][col + 1] == 1) cnt++;
        return cnt;
    }
}