# Time: O(m*n)
# Space: O(m*n)
class Solution:
    def gameOfLife(self, board: List[List[int]]) -> None:
        """
        Do not return anything, modify board in-place instead.
        """
        nrows, ncols = len(board), len(board[0])
        board_copy = [[None] * ncols for _ in range(nrows)]
        
        for i in range(nrows):
            for j in range(ncols):
                board_copy[i][j] = next_cell_state(board, i, j)
        
        # Copy new board values
        for i in range(nrows):
            for j in range(ncols):
                board[i][j] = board_copy[i][j]

def next_cell_state(board, i, j):
    current = board[i][j]
    total_alive = sum(get_cell_neighbours(board, i, j))
    
    # Rule 4: Exact 3 neighbors will mean dead cell becomes alive
    #         Live cell remains live
    if total_alive == 3:
        return 1
    
    # Rule 2: Live cell lives onto next generation
    #         Dead cell remains dead
    elif total_alive == 2:
        return current
    
    # Rules 1 and 2: Under-population and over-population
    return 0

# Return cell at (i, j) or 0 if it's out of bounds
def cell(board, i, j):
    nrows, ncols = len(board), len(board[0])
    
    return board[i][j] if 0 <= i < nrows and 0 <= j < ncols else 0

# Get surrounding 8 neighbours of cell at (i, j)
def get_cell_neighbours(board, i, j):
    return (
        cell(board, i - 1, j - 1), cell(board, i - 1, j), cell(board, i - 1, j + 1),
        cell(board, i, j - 1),                                    cell(board, i, j + 1),
        cell(board, i + 1, j - 1), cell(board, i + 1, j), cell(board, i + 1, j + 1)
    )