Leetcode 200. Number of Islands

 1 public class Solution {
 2     public int NumIslands(char[,] grid) {
 3         if(grid==null||grid.GetLength(0)==0||grid.GetLength(1)==0)
 4         {
 5             return 0;
 6         }
 7         int h = grid.GetLength(0);
 8         int w = grid.GetLength(1);
 9         int count = 0;
10         // Create 2D bool array to record the islands have been visited
11         bool[,] visit = new bool[h,w];
12         //find the first ‘1‘ on island and find all other ‘1‘s by calling Bfs;
13         for(int i=0; i<h; i++)
14         {
15             for(int j=0; j<w; j++)
16             {
17                 //only check unvisited ones
18                 if(!visit[i,j] && grid[i,j]==‘1‘)
19                 {
20                     count++;
21                     Bfs(grid, visit , i , j);
22                 }
23             }
24         }
25         return count;
26     }
27     //Breadth-first Search to find all ‘1‘s on this island and flip visit to true;
28     private void Bfs(char[,] grid, bool[,] visit, int row, int col)
29     {
30         int h = grid.GetLength(0);
31         int w = grid.GetLength(1);
32         if(row>=0&& row<h && col>=0 && col<w && !visit[row,col] && grid[row,col]==‘1‘)
33         {
34             //flip visit
35             visit[row,col]=true;
36             //element above 
37             Bfs(grid, visit, row-1, col);
38             //element below
39             Bfs(grid, visit, row+1, col);
40             //element left
41             Bfs(grid, visit, row, col-1);
42             //element right
43             Bfs(grid, visit, row, col+1);
44         }
45     }
46 }