易理解版八皇后

为了面试复习一下经典的题目

八皇后

当然有更短更精奇的写法，但是我觉得我这个比较容易理解吧？。。。

count = 0


def eight_queens(queens_position, depth):
    """
    Computer how many solutions are there for eight queens problem
    """

    def is_valid(board, pos):
        """
        Check if given position is valid
        """

        def isOnSameLine(pos1, pos2):
            """
            check if this two position is on diagonal or vertical line
            """
            if pos1[1] == pos2[1]:
                return True

            # Slope is 1
            # y = (x - a) + b
            if pos2[1] == (pos2[0] - pos1[0] + pos1[1]):
                return True

            # Slope is -1
            # y = -(x - a) + b
            if pos2[1] == (-(pos2[0] - pos1[0]) + pos1[1]):
                return True

            return False

        for lop in range(len(board)):
            if isOnSameLine((lop, board[lop]), pos):
                return False
        return True

    if depth == 8:
        print(queens_position)
        global count
        count += 1
        return

    # Trying to place queen
    for lop in range(8):
        if is_valid(queens_position, (len(queens_position), lop)):
            tmp_list = list(queens_position)
            tmp_list.append(lop)
            eight_queens(tmp_list, depth + 1)


if __name__ == '__main__':
    eight_queens([], 0)
    print(count)