class Solution {
public:
    void gameOfLife(vector<vector<int>>& board) {
        if (board.size() == 0) return;
        int boardi = board.size(), boardj = board[0].size();
        vector<vector<int>> ret(boardi, vector<int>(boardj));
        for (int i = 0; i < boardi; i++) {
            for (int j = 0; j < boardj; j++) {
                int ali = 0, now = board[i][j];
                for (int ii = i - 1; ii <= i + 1; ii++) {
                    if (ii < 0 || ii >= boardi) continue;
                    for (int jj = j - 1; jj <= j + 1; jj++) {
                        if (jj < 0 || jj >= boardj) continue;
                        if (board[ii][jj]) ali += 1;
                    }
                }
                ali -= now;
                if (now && ali < 2) now = 0;
                if (now && (ali == 2 || ali == 3)) now = 1;
                if (now && ali > 3) now = 0;
                if (!now && ali == 3) now = 1;
                ret[i][j] = now;
            }
        }
        board = ret;
    }
};