130. Surrounded Regions

Posted 2020-08-09 咖啡中不塌缩的方糖

Given a 2D board containing ‘X‘ and ‘O‘ (the letter O), capture all regions surrounded by ‘X‘.

A region is captured by flipping all ‘O‘s into ‘X‘s in that surrounded region.

For example,

X X X X
X O O X
X X O X
X O X X

 

After running your function, the board should be:

X X X X
X X X X
X X X X
X O X X

public void Solve(char[,] board) {
        if(board.GetLength(0)==0 || board.GetLength(0)==0 ) return;
        int rowLength = board.GetLength(0);
        int colLength = board.GetLength(1);
 
        for(int i = 0;i<rowLength;i++)
        {
            for(int j = 0;j<colLength;j++)
            {
                if((i==0||j==0||i == rowLength-1 || j == colLength -1)&&(board[i,j]==‘O‘))
                {
                    DFS(board,i,j);
                }
            }
        }
        for(int i = 0;i<rowLength;i++)
        {
            for(int j = 0;j<colLength;j++)
            {
               if(board[i,j]==‘T‘)  board[i,j]=‘O‘;
               else if(board[i,j]==‘O‘)  board[i,j]=‘X‘;
            }
        }
        return;
        
    }
    
    private void DFS(char[,] board, int row, int col)
    {
        board[row,col] = ‘T‘;
        if(row>0 && board[row-1,col] == ‘O‘) DFS(board,row-1,col);
        if(row<(board.GetLength(0)-1) && board[row+1,col] == ‘O‘) DFS(board,row+1,col);
        if(col>1 && board[row,col-1] == ‘O‘) DFS(board,row,col-1);
        if(col<(board.GetLength(1)-1) && board[row,col+1] == ‘O‘) DFS(board,row,col+1);
    }