dfs笔记,为什么,网格的深度优先搜索java板

130. 被围绕得区域Tuesday, August 31, 20219:01 AMclass Solution {    public void solve(char[][] board) {        // 思路：从外围走。如果是o 把他改为*        // 路径，上下左右搜索。其他也可可以。        // dfs         // 重新遍历。输出结果。把o 改为x, 把* 改为o                if (board == null || board.length == 0) return;        int m = board.length;        int n = board[0].length;        for (int i = 0; i < m; i++) {            for (int j = 0; j < n; j++) {                // 从边缘o开始搜索                if( (i == 0 || j == 0|| i== m-1 || j == n-1) && board[i][j] == 'O'){                    // board[i][j] = '*'                    // dfs(board[i][j]);//这样写。传入得是一个char , 所以不行，得加两个参入参数，i， j                    dfs(board, i, j);                }            }        }        for (int i = 0; i < m; i++) {            for (int j = 0; j < n; j++) {                if (board[i][j] == 'O') {                    board[i][j] = 'X';                }                if (board[i][j] == '*') {                    board[i][j] = 'O';                }            }        }    }    // private void dfs(char[][] board){        private void dfs(char[][] board, int i , int j){                //一定要写递归终止条件        if (i < 0 || j < 0 || i >= board.length  || j >= board[0].length || board[i][j] == 'X' || board[i][j] == '*') {            // board[i][j] == '*' 说明已经搜索过了.             return;        }                // (i = 0 || j = 0|| i= m-1 || j = n-1)边界位置                board[i][j] = '*';                // 深搜，定义路径        // dfs(board[i-1][j]); 这样写不行        // dfs(board[i+1][j]);        // dfs(board[i][j-1]);        // dfs(board[i][j+1]);        dfs(board,i-1,j);        dfs(board,i+1,j);        dfs(board,i,j-1);        dfs(board,i,j+1);    }}