LeetCode #463 - 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，即计算二维网格中岛屿的周长。通过遍历矩阵并检查每个为1的元素周围环境来确定其对总周长的贡献。

题目描述：

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.

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:

对于矩阵中每个为1的元素，根据它所处的位置，判断它的上下左右是不是岛屿的边界，如果是就可以让周长加一。

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