Island Perimeter

最新推荐文章于 2021-03-04 06:20:03 发布

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本文介绍了一个算法问题：计算二维网格中岛屿的周长。通过遍历每个单元格并检查其相邻单元格的状态来确定周长。

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:

Input:
[[0,1,0,0],
[1,1,1,0],
[0,1,0,0],
[1,1,0,0]]

Output: 16

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

在这里插入图片描述

题目很好理解，让我们求岛的周长。其中，题目限定了只有一个岛，我们可以逐个grid遍历，对每个格子访问四周，若果是水，周长+1，若果格子是边界，那么周长也+1。

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