floodfill算法系列一＞被围绕的区域

整体思想：

代码设计：

代码呈现：

class Solution {int m,n;int[] dx = {0,0,-1,1};int[] dy = {-1,1,0,0};public void solve(char[][] board) {m = board.length;n = board[0].length;//先扫描边界，把不满足题意的连通块变为'.'for(int i = 0; i < n; i++){if(board[0][i] == 'O') dfs(board,0,i);if(board[m-1][i] == 'O') dfs(board,m-1,i);}for(int j = 0; j < m; j++){if(board[j][0] == 'O') dfs(board,j,0);if(board[j][n-1] == 'O') dfs(board,j,n-1);}//最后把'.'改会'o',把'o'改为'X'for(int i = 0; i < m; i++)for(int j = 0; j < n; j++){if(board[i][j] == 'O')board[i][j] = 'X';else if(board[i][j] == '.')  board[i][j] = 'O';}}private void dfs(char[][] board, int i, int j){board[i][j] = '.';for(int k = 0; k < 4; k++){int x = dx[k] + i; int y = dy[k] + j;if(x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'O'){dfs(board,x,y);}}}
}