leetcode 130. Surrounded Regions

  

public void solve(char[][] board) {
if(board==null || board.length<=1 || board[0].length<=1){
return;
}
for(int i=0;i<board[0].length;i++){
fill(board, 0, i);
fill(board, board.length-1, i);
}
for(int i=0;i<board.length;i++){
fill(board, i, 0);
fill(board, i, board[0].length-1);
}
for(int i=0;i<board.length;i++){
for(int j=0;j<board[0].length;j++){
if(board[i][j]=='O'){
board[i][j]='X';
}
else if(board[i][j]=='#'){
board[i][j]='O';
}
}
}


}

public void fill(char[][] board, int i, int j) {
if (board[i][j] != 'O') {
return;
}
board[i][j] = '#';
LinkedList<Integer> queue = new LinkedList<Integer>();
int code = i * board[0].length + j;
queue.offer(code);
while (!queue.isEmpty()) {
code=queue.poll();
int row=code/board[0].length;
int col=code%board[0].length;
if(row>0 && board[row-1][col]=='O'){
queue.offer((row-1)*board[0].length+col);
board[row-1][col]='#';
}
if(row<board.length-1 && board[row+1][col]=='O'){
queue.offer((row+1)*board[0].length+col);
board[row+1][col]='#';
}
if(col>0 && board[row][col-1]=='O'){
queue.offer((row)*board[0].length+col-1);
board[row][col-1]='#';
}
if(col<board[0].length-1 && board[row][col+1]=='O'){
queue.offer((row)*board[0].length+col+1);
board[row][col+1]='#';
}

}
}