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).
解法一：利用构造函数求解：
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=NULL;
return Temp::GetSum();
}
解法二：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;
}
解法三：利用函数指针求解
typedef unsigned int (*fun)(unsigned int);
unsigned int Solution3_Teminator(unsigned int n)
{return 0;}
unsigned int Sum_Solution3(unsigned int n)
{
static fun f[2]={Solution3_Teminator,Sum_Solution3};
return n+f[!!n](n-1);
}
解法四：利用类模板求解
template<unsigned int n> struct Sum_Solution4
{
enum Value {N=Sum_Solution4<n-1>::N +n};
}；
template<> struct Sum_Solution4<1>
{
enum Value{N=1};
};