LeetCode - 463. Island Perimeter - O(MN)- (C++) - 解题报告

原题

原题链接

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:

给定一个二维整数的方格地图，1代表陆地，0代表有水的地方。每个方格都是垂直或者水平连接的，没有斜线。被水包围的中间有一个小岛（小岛可能包含了很多个的陆地方格），小岛里没有岛中湖（内部的水和外部的水是连通的）。每个方格单元的边长都是1。各个地方都是成直角的，长度宽度不超过100，判断小岛的边长。

思路

判断其四面是否有陆地，四面都有陆地的对周长无贡献，两面有陆地的贡献周长为2，一面有陆地的贡献周长为3，四面都没有陆地的贡献周长为4。

代码

class Solution {
public:
    int islandPerimeter(vector<vector<int>>& grid) {
        int sum=0;
        int m=grid.size(),n=grid[0].size();
        for(int i=0;i<m;i++)
            for(int j=0;j<n;j++)
                if(grid[i][j]){ 
                if(i==0||grid[i-1][j]==0) sum++;
                if(i==m-1||grid[i+1][j]==0) sum++;
                if(j==0||grid[i][j-1]==0) sum++;
                if(j==n-1||grid[i][j+1]==0) sum++;
                }
        return sum;
    }
};