[LeetCode] Game of Life

A solution using additional spaces to solve a copy of the original board is easy. To get an in-place solution, we need to record the information of state transitions directly in the board.

We record the state transitions as follows:

// States:
//  0 : dead to dead
//  1 : live to live
//  2 : live to dead
//  3 : dead to live

The code is as follows.

 1 class Solution {
 2 public:
 3     void gameOfLife(vector<vector<int>>& board) {
 4         int m = board.size(), n = m ? board[0].size() : 0;
 5         int di[8] = {-1, -1, -1,  0, 0,  1, 1, 1};
 6         int dj[8] = {-1,  0,  1, -1, 1, -1, 0, 1};
 7         for (int i = 0; i < m; i++) {
 8             for (int j = 0; j < n; j++) {
 9                 int live = 0;
10                 for (int k = 0; k < 8; k++) {
11                     int ii = i + di[k], jj = j + dj[k];
12                     if (ii < 0 || ii >= m || jj < 0 || jj >= n) continue;
13                     if (board[ii][jj] == 1 || board[ii][jj] == 2) live++;
14                 }
15                 if (board[i][j] == 1 && (live < 2 || live > 3)) board[i][j] = 2;
16                 else if (!board[i][j] && live == 3) board[i][j] = 3;
17             }
18         }
19         for (int i = 0; i < m; i++)
20             for (int j = 0; j < n; j++)
21                 board[i][j] %= 2;
22     }
23 };

Wanna a shorter one? Stefan always does so :-) 

posted @ 2015-10-04 00:59  jianchao-li  阅读(699)  评论(0)  编辑  收藏  举报