[leetcode]: 463. Island Perimeter

1.题目
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).
翻译：给一个0-1矩阵，1-表示陆地，求1连接成的岛屿的周长。
例：
[[0,1,0,0],
[1,1,1,0],
[0,1,0,0],
[1,1,0,0]]
周长：16

2.分析
明显一个方格贡献的边长=4-重合的边
遍历一遍矩阵，找出每个1元素的相邻元素个数。
3.代码
c++

int islandPerimeter(vector<vector<int>>& grid) {    int perimeter = 0;    for (int i = 0; i < grid.size();i++) {        for (int j = 0; j < grid[0].size();j++) {            if (grid[i][j] == 1) {                perimeter += 4;                //上                if (i - 1 >= 0 && grid[i - 1][j] == 1)                    perimeter--;                //下                if (i + 1 < grid.size() && grid[i + 1][j] == 1)                    perimeter--;                //左                if (j - 1 >= 0 && grid[i][j - 1] == 1)                    perimeter--;                //右                if (j + 1 < grid[0].size() && grid[i][j + 1] == 1)                    perimeter--;            }        }    }    return perimeter;}

solution里提供的答案是只需要考虑上，左即可，最后乘以2就行啦。

if(i!=0 && grid[i-1][j] == 1) repeat++;if(j!=0 && grid[i][j-1] == 1) repeat++;return 4*count-repeat*2;