LeetCode-Easy部分标签为HashTable 463. Island Perimeter

原文

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:

题目分析

1代表陆地，0代表海洋，恰好有1整块陆地区域。若某块区域为海洋，则无有效边；若某块为陆地，有效边最多为3个， 有效边最少为0个。若某块陆地紧邻1块其他陆地，则次陆地有效边为3个，若紧邻2块，则有效边为2个，若紧邻3块其他陆地，则有效边为1个，若紧邻4块，有效边为0个。

代码实现

       public int LandPerimeter(int[,] grid)
       {
           int rtn=0;
           for(int i=0; i<=grid.GetUpperBound(0);i++)
           {
               for(int j=0;j<=grid.GetUpperBound(1);j++)
               {
                   if (grid[i, j] == 1)
                       rtn +=4-surroundingIsland(grid,i,j);
               }
           }
           return rtn;
       }

       //获取某个网格周围的网格数（[0,4]）
       //noy: y向网格索引（行）
       //nox：x向网格索引（列）
       private int surroundingIsland(int[,] grid, int noy, int nox)
       {
           int rtnCnt=0;
           if (nox > 0)
           {
               if (grid[noy, nox - 1] == 1)
                   rtnCnt++;
           }
           if (nox < grid.GetUpperBound(1))//nox小于（列）最大索引吗
           {
               if (grid[noy, nox + 1] == 1)
                   rtnCnt++;
           }
           if (noy > 0)
           {
               if (grid[noy - 1, nox] == 1)
                   rtnCnt++;
           }
           if(noy<grid.GetUpperBound(0))//noy小于最大（行）索引吗
           {
               if (grid[noy + 1, nox] == 1)
                   rtnCnt++;
           }
           return rtnCnt;
       }

时间复杂度和空间复杂度都为O(n^2)，因为是二维数组，所以可以接受。

更多参考

LeetCode-Easy部分中标签为HashTable的所有题目