算法

用到了位运算 ,原地更新就是在原数组更新，
二进制10表示由0变成1，即10进制2
二进制11 表示由1变成1 ，即10进制3
二进制01表示由1变成0，即10进制1
最后只要输出左边的1位即可，可以用位运算>>1加快效率

C++ 代码

class Solution {
public:
    void gameOfLife(vector<vector<int>>& board) {
        int m = board.size();
        if (m==0) return;
        int n = board[0].size();
        int new_x, new_y, live;
        int dx[] = {-1,-1,-1, 0, 1, 1,  1, 0 };
        int dy[] = {-1, 0, 1, 1, 1, 0, -1, -1};
        for (int i=0; i<m; i++)
            for (int j=0; j<n; j++) {
               live = 0;
               for (int k=0; k<8; k++){
                    new_x =  i+dx[k];
                    new_y = j + dy[k];
                    if (new_x >= 0 and new_x < m and new_y >=0 and new_y < n) {
                        if (board[new_x][new_y] & 1) live++;
                    }
                }
               if (board[i][j] & 1 and live < 2 ) board[i][j] = 1;
               if (board[i][j] & 1 and (live == 2 || live == 3 )) board[i][j] = 3;
               if (board[i][j] & 1 and live > 3) board[i][j] = 1;
               if (!(board[i][j] & 1)  and live == 3 ) board[i][j] = 2;
            }
        for (int i=0; i<m; i++)
            for (int j=0; j<n; j++)    
                board[i][j] = board[i][j] >> 1;

    }
};