leetcode-go/medium/289.game-of-life.go

func gameOfLife(board [][]int) {
	m, n := len(board), len(board[0])
	xDir := []int{1, 1, 0, -1, -1, -1, 0, 1}
	yDir := []int{0, -1, -1, -1, 0, 1, 1, 1}
	for y := 0; y < m; y++ {
		for x := 0; x < n; x++ {
			cnt := 0
			for i := 0; i < 8; i++ {
				xPos, yPos := x+xDir[i], y+yDir[i]
				if 0 <= xPos && xPos < n && 0 <= yPos && yPos < m {
					cnt += board[yPos][xPos] & 1
				}
			}
			if cnt == 2 {  // Keep current state
				board[y][x] |= (board[y][x] & 1) << 1
			} else if cnt == 3 {  // Live :-)
				board[y][x] |= 2
			}  // Else, die X-(
		}
	}
	for y := 0; y < m; y++ {
		for x := 0; x < n; x++ {
			board[y][x] >>= 1
		}
	}
}