algorithm-class/大厂刷题班/class34/Problem_0289_GameOfLife.java

package class34;

// 有关这个游戏更有意思、更完整的内容：
// https://www.bilibili.com/video/BV1rJ411n7ri
// 也推荐这个up主
public class Problem_0289_GameOfLife {

	public static void gameOfLife(int[][] board) {
		int N = board.length;
		int M = board[0].length;
		for (int i = 0; i < N; i++) {
			for (int j = 0; j < M; j++) {
				int neighbors = neighbors(board, i, j);
				if (neighbors == 3 || (board[i][j] == 1 && neighbors == 2)) {
					board[i][j] |= 2;
				}
			}
		}
		for (int i = 0; i < N; i++) {
			for (int j = 0; j < M; j++) {
				board[i][j] >>= 1;
			}
		}
	}

	// b[i][j] 这个位置的数，周围有几个1
	public static int neighbors(int[][] b, int i, int j) {
		return f(b, i - 1, j - 1)
				+ f(b, i - 1, j)
				+ f(b, i - 1, j + 1)
				+ f(b, i, j - 1)
				+ f(b, i, j + 1)
				+ f(b, i + 1, j - 1)
				+ f(b, i + 1, j)
				+ f(b, i + 1, j + 1);
	}

	// b[i][j] 上面有1，就返回1，上面不是1，就返回0
	public static int f(int[][] b, int i, int j) {
		return (i >= 0 && i < b.length && j >= 0 && j < b[0].length && (b[i][j] & 1) == 1) ? 1 : 0;
	}

}