被自己蠢哭了。
visit[i][j] = true写成了visit[j][j] = true 我DEBUG了1个多小时。。。。。。。
从最外面那圈的所有O开始顺着相邻的O走，里面那些能走到的O就是不用变成反革命分子的。否则最后变成X，反革命分子。
主要是剪枝，乱七八糟一大堆情况，包括但不限于：
走到边了，走出界了，已经接受过组织的审查了， 他本身就是反革命分子，etc..
一开始4*4 test case没问题让我以为代码是正确的。结果后来各种stackoverflow，以为是不够好，改了依然如此，绝望中浪费了整整他妈的一个多小时。
public class Solution
{
public void solve(char[][] board)
{
if(board.length == 0) return;
boolean[][] moveVisit = new boolean[board.length][board[0].length];
boolean[][] ok = new boolean[board.length][board[0].length];
for(int i = 0; i < board.length;i++)
{
if(board[i][0] == 'O')
{
go(board,moveVisit,ok,i,0,true);
moveVisit = new boolean[board.length][board[0].length];
}
if(board[i][board[0].length-1] == 'O')
{
go(board,moveVisit,ok,i,board[0].length-1,true);
moveVisit = new boolean[board.length][board[0].length];
}
}
for(int i = 1; i < board[0].length;i++)
{
if(board[0][i] == 'O')
{
go(board,moveVisit,ok,0,i,true);
moveVisit = new boolean[board.length][board[0].length];
}
if(board[board.length-1][i]== 'O')
{
go(board,moveVisit,ok,board.length-1,i,true);
}
}
for(int i = 1; i < board.length-1;i++)
{
for(int j = 1; j < board[0].length-1;j++)
{
if(board[i][j] == 'X') continue;
if(!ok[i][j]) board[i][j] = 'X';
}
}
return;
}
public void go(char[][] board, boolean[][] moveVisit, boolean[][] ok, int i, int j,boolean begin)
{
if(board[i][j] == 'X' || moveVisit[i][j]) return;
if(!begin && (i == 0 || j == 0 || i == board.length-1 || j == board[0].length -1)) return;
ok[i][j] = true;
moveVisit[i][j] = true;
if(i > 0 && board[i-1][j] == 'O') go(board,moveVisit,ok,i-1,j,false);
if(j>0 && board[i][j-1] == 'O') go(board,moveVisit,ok,i,j-1,false);
if(i < board.length-1 && board[i+1][j] == 'O') go(board,moveVisit,ok,i+1,j,false);
if(j < board[0].length-1 && board[i][j+1] == 'O') go(board,moveVisit,ok,i,j+1,false);
return;
}
}