Number of Islands

 

 

 Number of Islands

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

 

Example 1:

Input: grid = [
  ["1","1","1","1","0"],
  ["1","1","0","1","0"],
  ["1","1","0","0","0"],
  ["0","0","0","0","0"]
]
Output: 1

Example 2:

Input: grid = [
  ["1","1","0","0","0"],
  ["1","1","0","0","0"],
  ["0","0","1","0","0"],
  ["0","0","0","1","1"]
]
Output: 3

Number of Islands

class Solution {
public:
  bool  dfs(vector<vector<char> > &v,int i,int j,int n,int m)
  {
      if(i<0||j<0||j>=m||i>=n||v[i][j]=='0'||v[i][j]=='2')
          return false;
      v[i][j]='2';
      dfs(v,i,j-1,n,m);
      dfs(v,i,j+1,n,m);
      dfs(v,i-1,j,n,m);
      dfs(v,i+1,j,n,m);
      return true;
     
  }
    int numIslands(vector<vector<char>>& grid) {
        int ans=0;
        for(int i=0;i<grid.size();++i)
        {
           
            for(int j=0;j<grid[i].size();++j)
            {
                if(grid[i][j]=='1')
                {
                    if(dfs(grid,i, j, grid.size(),grid[0].size()))
                        ++ans;
                }
            }
        }
        return ans;
       
       
    }
};