"""
输入正整数n,计算从集合0,1....n当中可以组成的偶数的数量(偶数中不能有重复的数值)
"""
class Solution:
    def get_even_num(self, n):
        # write code here
        if n == 0:
            return 1
        ou = n // 2 + 1
        result = ou

        for i in range(1, n + 1):
            step = i
            a = ou
            while step>0:
                a = a*(n-step+1)
                step -= 1
            b = ou-1
            if i-1>0:
                step = n-1
                count = i-1
                # print("step:",step,"count:", count)
                while count>0:
                    b = b*step
                    count -= 1
                    step -= 1
            result += a-b
            # print(a,b)
        # print(result)
        return result
Solution().get_even_num(4)