dfs 栈溢出，bfs超时，用dfs非递归就不溢出了，前后写了1一个星期
class node{    int i;    int j;        public node(int i1,int j1)    {        i=i1;        j=j1;                   }}    public class Solution {    public void solve(char[][] board) {               int len1=board.length;        if(len1<=0)return;        int len2=board[0].length;        if(len1<=2||len2<=2) return;        for(int i=0;i<len1;i++)        {            if(board[i][0]==‘O‘) dfs(board,i,0);            if(board[i][len2-1]==‘O‘) dfs(board,i,len2-1);                    }        for(int i=0;i<len2;i++)        {                        if(board[0][i]==‘O‘)dfs(board,0,i);            if(board[len1-1][i]==‘O‘)dfs(board,len1-1,i);        }        for(int i=0;i<len1;i++)        {            for(int j=0;j<len2;j++)            {                if(board[i][j]==‘h‘) board[i][j]=‘O‘;                else  board[i][j]=‘X‘;            }        }                    }    public boolean is(int i,int j,int len1,int len2)    {        if(i>=0&&i<len1&&j>=0&&j<len2) return true;        return false;                    }    public void dfs(char b[][],int i,int j)    {        int len1=b.length;        int len2=b[0].length;       Stack<node> s=new Stack<node>();       b[i][j]=‘h‘;       s.push(new node(i,j));                                                 }}