[力扣题解] 463. 岛屿的周长

题目：463. 岛屿的周长

思路

深度优先搜索；

代码

Method 1

对于遍历到的一个地块，向四周探索，越界或者遇到海洋地块说明这条边需要统计；

class Solution {
private:
    int dir[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
    int result = 0; // 周长
    void dfs(vector<vector<int>>& grid, vector<vector<bool>>& vistied, int x, int y)
    {
        int m = grid.size(), n = grid[0].size();
        int i, j;
        int next_x, next_y;

        for(i = 0; i < 4; i++)
        {
            next_x = x + dir[i][0];
            next_y = y + dir[i][1];
            if(next_x < 0 || next_x >= m || next_y < 0 || next_y >= n)
            {
                result++;
                continue;
            }
            if(grid[next_x][next_y] == 0)
            {
                result++;
            }
            if(!vistied[next_x][next_y] && grid[next_x][next_y] == 1)
            {
                vistied[next_x][next_y] = true;
                dfs(grid, vistied, next_x, next_y);
            }
        }
    }

public:
    int islandPerimeter(vector<vector<int>>& grid) {
        int m = grid.size(), n = grid[0].size();
        int i, j;
        vector<vector<bool>> vistied(m, vector<bool>(n, false));

        for(i = 0; i < m; i++)
        {
            for(j = 0; j < n; j++)
            {
                if(!vistied[i][j] && grid[i][j] == 1)
                {
                    vistied[i][j] = true;
                    dfs(grid, vistied, i, j);
                }
            }
        }
        return result;
    }
};

Method 2

初始周长 = 岛屿地块 * 4，在岛屿内部，有一对相邻地块，周长-2；