Game of Life Solutions in C++

// Source : https://leetcode.com/problems/game-of-life/
// Author : Hao Chen
// Date   : 2019-03-20




class Solution {
public:
    // the problem here is we need store two states in one cell,
    // one is the original state, another is the new state
    // So, we could store the state into the bit.
    //  - Old State: the first  bit from the right
    //  - New State: the second bit from the right
    void liveCheck(vector<vector<int>>& board, int r, int c) {
        int cnt = 0;
        for (int i=r-1; i<=r+1; i++) {
            if (i < 0 || i>=board.size()) continue;
            for (int j=c-1; j<=c+1; j++) {
                if (j<0 || j>=board[0].size() || (i==r && j==c)) continue;
                if ( board[i][j] & 1 ) cnt++;
            }
        }

        //live -> die
        //if (board[r][c]==1 && (cnt < 2 || cnt > 3)) board[r][c] = 1;

        //live -> live
        if ( board[r][c] == 1 && (cnt == 2 || cnt == 3) ) board[r][c] = 3;

        //die -> live
        if ( board[r][c] == 0 && cnt == 3 ) board[r][c] = 2;

    }

    void gameOfLife(vector<vector<int>>& board) {
        for (int i=0; i<board.size(); i++) {
            for (int j=0; j<board[0].size(); j++) {
                liveCheck(board, i, j);
            }
        }

        for (int i=0; i<board.size(); i++) {
            for (int j=0; j<board[0].size(); j++) {
                board[i][j] >>= 1;
            }

        }

    }
};