八皇后DFS

def solve(____):
    def is_valid(____):
        for i in range(____):
            if board[i] == col or abs(____) == row - i:
                return False
        return True
    count = ____
    def backtrack(____):
        nonlocal count
        if row == n:
            count += ____
            return
        for col in range(____):
            if is_valid(____):
                board[row] = col
                backtrack(____)
    backtrack(____, [____] * n)
    print(____)