用位运算节省空间

0X00 例子

• 动态规划的空间优化（滚动数组）

0 ^ 1 = 0 1 ^ 1 = 0

• 少状态时用位运算在原地记录状态

289. 生命游戏

class Solution:
    def gameOfLife(self, board: List[List[int]]) -> None:
        if not len(board): return
        m, n = len(board), len(board[0])
        for i in range(m):
            for j in range(n):
                s = board[i][j]
                cnt = 0
                for x in range(i-1, i+2):
                    for y in range(j-1, j+2):
                        if x < 0 or y < 0 or x >= m or y >= n: continue
                        if x == i and y == j: continue
                        if board[x][y] & 1: cnt += 1
                # print(cnt)
                if s & 1:
                    if cnt < 2 or cnt > 3: s |= 4
                    else: s |= 8
                else:
                    if cnt == 3: s |= 2
                    else: s |= 16
                board[i][j] = s
        
        # print(board)
        for i in range(m):
            for j in range(n):
                s = board[i][j]
                if s & 2 or s & 8: s = 1 
                else: s = 0
                board[i][j] = s