Surrounded Regions 感染列岛

Given a 2D board containing 'X' and '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

感染列岛 哈哈

挺有意思一道题，讲解 和code http://www.cnblogs.com/huntfor/p/3898068.html

题解

// XXXXX -->  X X X X X --> XXXX
// XOXOX 　　 X# X O X 　　XOXX
// XOXOX 　　 X# X O X　　 XOXX
// XOXXX  　　X# X X X　　 XOXX

用queue来存储，这样后面加进来的传染源就不会干扰之前的传染源传染

public class Solution {

    public void solve(char[][] board) {

        if(board==null||board.length<=1||board[0].length<=1 ) return;

        for(int i=0;i<board.length;i++){ // fist col

            helper(board, i, 0);

            helper(board, i, board[0].length-1); // last col

        }

        for(int j=0;j<board[0].length;j++){ //first row

            helper(board, 0, j);

             helper(board, board.length-1, j); // last row

        }

        for(int i=0;i<board.length;i++){

            for(int j=0;j<board[0].length;j++){

                if(board[i][j]!='#'){

                    board[i][j] = 'X';

                }else

                    board[i][j] = 'O';

            }

        }

    }

    private void helper(char[][] b, int i, int j){

        if(b[i][j]!='O') return;

        b[i][j]='#';

        int code = b[0].length*i+j;

        

        LinkedList<Integer> queue = new LinkedList<Integer>(); // 为了从外围逐渐向中心渲染

        queue.add(code);

        while(!queue.isEmpty()){

            int c = queue.poll();

            int row = c/b[0].length;

            int col = c%b[0].length;

            //up

            if(row>0 && b[row-1][col]=='O'){

                b[row-1][col]='#';

                queue.add(b[0].length*(row-1)+col);

            }

            //down

            if(row<b.length-1 && b[row+1][col]=='O'){

                b[row+1][col]='#';

                queue.add(b[0].length*(row+1)+col);

            }

            //left

            if(col>0 && b[row][col-1]=='O'){

                b[row][col-1]='#';

                queue.add(b[0].length*(row)+col-1);

            }

            //right

            if(col< b[0].length-1 && b[row][col+1]=='O'){

                b[row][col+1]='#';

                queue.add(b[0].length*(row)+col+1);

            }

        }

    }

}