diconnectIsland.txt

1568. Minimum Number of Days to Disconnect Island

You are given an m x n binary grid grid where 1 represents land and 0 represents water. 
An island is a maximal 4-directionally (horizontal or vertical) connected group of 1's.

The grid is said to be connected if we have exactly one island, otherwise is said disconnected.

In one day, we are allowed to change any single land cell (1) into a water cell (0).

Return the minimum number of days to disconnect the grid.

class Solution {
private:
    int totalLand(vector<vector<int>>& grid)
    {
        int n = grid.size() , m = grid[0].size();
        vector<vector<int>>vis(n,vector<int>(m,0));
        int count = 0;

        for (int i=0;i<n;i++)
        {
            for (int j=0;j<m;j++)
            {
                if (grid[i][j] == 1 and !vis[i][j])
                {
                    queue<pair<int,int>>q;
                    vis[i][j] = 1;
                    q.push({i,j});
                    count += 1;
                    
                    while(!q.empty())
                    {
                        int row = q.front().first;
                        int col = q.front().second;
                        q.pop();

                        int delrow [] = {-1,0,+1,0};
                        int delcol [] = {0,1,0,-1};
                        for (int i=0;i<4;i++)
                        {
                            int nrow = row + delrow[i];
                            int ncol = col + delcol[i];
                            if (nrow >=0 and nrow < grid.size() and ncol >= 0 and ncol < grid[0].size() and !vis[nrow][ncol] and grid[nrow][ncol] == 1)
                            {
                                q.push({nrow,ncol});
                                vis[nrow][ncol] = 1;
                            }
                        }
                    }
                }
            }
        }
       
        return count;
    }
public:
    int minDays(vector<vector<int>>& grid) 
    {
        int initialLand = totalLand(grid);
        if (initialLand == 0 or initialLand >= 2)   return 0;
        
        for (int i=0;i<grid.size();i++)
        {
            for (int j=0;j<grid[0].size();j++)
            {
                if (grid[i][j] == 1)
                {
                    grid[i][j] = 0;
                    int newLand = totalLand(grid);
                    if (newLand != 1)   return 1;
                    grid[i][j] = 1;
                }
            }
        }
        
        return 2;
    }
};