leetcode--SurroundedRegions

思路：利用bfs先把所有和最外層O連通的O標記，然後遍歷所有點，沒被標記的O就是被X包圍的內層點

import java.util.LinkedList;
import java.util.Queue;

/**
 * Created by marsares on 15/6/28.
 */
public class SurroundedRegions {
    boolean[][]marked;
    boolean[][]zeros;
    int row;
    int column;
    public void solve(char[][] board) {
        if(board==null)return;
        if(board.length==0)return;
        row=board.length;
        column=board[0].length;
        zeros=new boolean[row][column];
        for(int i=0;i<column;i++){
            if(!zeros[0][i]&&board[0][i]=='O')bfs(0,i,board);
            if(!zeros[row-1][i]&&board[row-1][i]=='O')bfs(row-1,i,board);
        }
        for(int i=0;i<row;i++){
            if(!zeros[i][0]&&board[i][0]=='O')bfs(i,0,board);
            if(!zeros[i][column-1]&&board[i][column-1]=='O')bfs(i,column-1,board);
        }
        for(int i=0;i<row;i++){
            for(int j=0;j<column;j++){
                if(board[i][j]=='O'&&!zeros[i][j])board[i][j]='X';
            }
        }
    }
    public void bfs(int i,int j,char[][]board){
        Queue<Integer>queue=new LinkedList<Integer>();
        queue.add(i*column+j);
        zeros[i][j]=true;
        while(!queue.isEmpty()){
            int local=queue.poll();
            int x=local/column;
            int y=local%column;
            if(x-1>=0){
                if(board[x-1][y]=='O'&&!zeros[x-1][y]){
                    queue.add((x-1)*column+y);
                    zeros[x-1][y]=true;
                }
            }
            if(x+1<row){
                if(board[x+1][y]=='O'&&!zeros[x+1][y]){
                    queue.add((x+1)*column+y);
                    zeros[x+1][y]=true;
                }
            }
            if(y-1>=0){
                if(board[x][y-1]=='O'&&!zeros[x][y-1]){
                    queue.add(x*column+y-1);
                    zeros[x][y-1]=true;
                }
            }
            if(y+1<column){
                if(board[x][y+1]=='O'&&!zeros[x][y+1]){
                    queue.add(x*column+y+1);
                    zeros[x][y+1]=true;
                }
            }
        }
    }
    public void printBoard(char[][]board){
        for(int i=0;i<board.length;i++){
            for(int j=0;j<board[0].length;j++){
                System.out.print(board[i][j]);
            }
            System.out.println();
        }
    }
    public void printZeros(){
        for(int i=0;i<zeros.length;i++){
            for(int j=0;j<zeros[0].length;j++){
                System.out.print(zeros[i][j]);
            }
            System.out.println();
        }
    }
    public static void main(String[]args){
        SurroundedRegions sr=new SurroundedRegions();
        char[][]board={{'X','O','X','O','X','O'},{'O','X','O','X','O','X'},{'X','O','X','O','X','O'},{'O','X','O','X','O','X'}};
        sr.solve(board);
        sr.printBoard(board);
    }
}