package q289

func countLiveNeighbors(board [][]int, row, col int) int {
	cnt := 0
	for r := row - 1; r <= row+1; r++ {
		for c := col - 1; c <= col+1; c++ {
			if r == row && c == col || r < 0 || c < 0 || r >= len(board) || c >= len(board[0]) {
				continue
			}
			cnt += board[r][c] & 1
		}
	}
	return cnt
}

func gameOfLife(board [][]int) {
	for r := range board {
		for c := range board[r] {
			neighbors := countLiveNeighbors(board, r, c)
			if board[r][c]&1 == 1 {
				switch {
				case neighbors < 2 || neighbors > 3:
					// die
				default:
					board[r][c] |= 2 // survive
				}
			} else if neighbors == 3 {
				board[r][c] |= 2 // birth
			}
		}
	}

	// Next generation
	for r := range board {
		for c := range board[r] {
			board[r][c] >>= 1
		}
	}
}

var _ = gameOfLife