public void gameOfLife(int[][] board) {

if (board == null || board.length == 0) return;

int m = board.length, n = board[0].length;

for (int i = 0; i < m; i++) {

for (int j = 0; j < n; j++) {

int lives = liveNeighbors(board, m, n, i, j);

// In the beginning, every 2nd bit is 0;

// So we only need to care about when will the 2nd bit become 1.

if (board[i][j] == 1 && lives >= 2 && lives <= 3) {

board[i][j] = 3; // Make the 2nd bit 1: 01 ---> 11

}

if (board[i][j] == 0 && lives == 3) {

board[i][j] = 2; // Make the 2nd bit 1: 00 ---> 10

}

}

}

for (int i = 0; i < m; i++) {

for (int j = 0; j < n; j++) {

board[i][j] >>= 1; // Get the 2nd state.

}

}

}

public int liveNeighbors(int[][] board, int m, int n, int i, int j) {

int lives = 0;

for (int x = Math.max(i - 1, 0); x <= Math.min(i + 1, m - 1); x++) {

for (int y = Math.max(j - 1, 0); y <= Math.min(j + 1, n - 1); y++) {

lives += board[x][y] & 1;

}

}

lives -= board[i][j] & 1;

return lives;

}