Method factorial

AwesomeAlgorithms/CatalanNumber.py:17–21

(self, n)

        return self.factorial(n << 1) // (self.factorial(n) * self.factorial(n + 1))
    # 定义一个函数求取n的阶乘
    def factorial(self, n):
        result = 1
        for i in range(1, n + 1):
            result *= i
        return result

s = Solution()
print(s.numTrees(0))