leetcode--SurroundedRegions

来源：互联网发布：数据中心网络拓扑结构编辑：程序博客网时间：2024/06/07 02:07
思路：利用bfs先把所有和最外层O连通的O标记，然后遍历所有点，没被标记的O就是被X包围的内层点
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);    }}
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