Island Perimeter问题及解法

问题描述：

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.

示例：

[[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:

问题分析：

求解岛屿的周长，我们对一每一块cell的周长都记为4，它每与一块cell相连接，周长就减一。

过程详见代码：

class Solution {
public:
    int islandPerimeter(vector>& grid) {
        int h = grid.size();
    	int l = grid[0].size();
    	int res = 0;
        for(int i = 0; i < h; i++)
        {
        	for(int j = 0; j < l; j++)
        	{
        		if(grid[i][j])
        			res += 4;
        		if(i - 1 >= 0 && grid[i][j] && grid[i - 1][j]) res--;
        		if(i + 1 < h && grid[i][j] && grid[i + 1][j]) res--;
        		if(j - 1 >= 0 && grid[i][j] && grid[i][j - 1]) res--;
        		if(j + 1 < l && grid[i][j] && grid[i][j + 1]) res--;
			}
		}
		return res;
    }
};