求1+2+…+n

题目：求1+2+…+n，要求不能使用乘除法、for、while、if、else、switch、case等关键字及条件判断语句（A?B:C）。

//用构造函数求解
class Temp
{
public:
	Temp()
	{
		++N;
		Sum += N;
	}
	static void Reset()
	{
		N = 0;
		Sum = 0;
	}
	static unsigned int GetSum()
	{
		return Sum;
	}
private:
	static unsigned int N;
	static unsigned int Sum;
};

unsigned int Temp::N = 0;
unsigned int Temp::Sum = 0;

unsigned int Sum_Solution1(unsigned int n)
{
	Temp::Reset();

	Temp* a = new Temp[n];
	
	delete[]a;
	a = nullptr;
	return Temp::GetSum();
}
//利用虚函数求解
class A;
A* Array[2];
class A
{
public:
	virtual unsigned int Sum(unsigned int n)
	{
		return 0;
	}
};
class B :public A
{
public:
	virtual unsigned int Sum(unsigned int n)
	{
		return Array[!!n]->Sum(n - 1) + n;
	}
};
int Sum_Solution2(int n)
{
	A a;
	B b;
	Array[0] = &a;
	Array[1] = &b;

	int value = Array[1]->Sum(n);

	return value;
}
//利用函数指针
typedef unsigned int(*fun)(unsigned int);

unsigned int Solution_Teminator(unsigned int n)
{
	return 0;
}


unsigned int Sum_Solution3(unsigned int n)
{
	static fun f[2] = { Solution_Teminator,Sum_Solution3 };
	return n + f[!!n](n - 1);
}
//利用模板类型求解
templatestruct Sum_Solution4
{
	enum Value { N = Sum_Solution4::N + n };
};
template<>struct Sum_Solution4<1>
{
	enum Value { N = 1 };
};