class Temp
{
private:
 static int N;
 static int Sum;
public:
 Temp() {   ++ N;   Sum += N;    }
 static void Reset() {   N = 0;   Sum = 0; }
 static int GetSum() {   return Sum;   }
};
int Temp::N = 0;    //靜態(tài)成員的值對(duì)所有的對(duì)象是一樣的。靜態(tài)成員可以被初始化，但只能在類體外進(jìn)行初始化。
int Temp::Sum = 0;
int solution1_Sum(int n)
{
 Temp::Reset();
 Temp *a = new Temp[n];
 delete []a;
 a = 0;
 return Temp::GetSum();
}

class A;
A* Array[2];
class A
{
public:
 virtual int Sum (int n) { return 0; }
};
class B: public A
{
public:
 virtual int Sum (int n) { return Array[!!n]->Sum(n-1)+n; }
};
int solution2_Sum(int n)
{
 A a;

 Array[0] = &a;
 Array[1] = &b;
 int value = Array[1]->Sum(n);
 return value;
}

typedef int (*fun)(int);
int solution3_f1(int i)
{
 return 0;
}
int solution3_f2(int i)
{
 fun f[2]={solution3_f1, solution3_f2};
 return i+f[!!i](i-1);
}

template <int n> struct solution4_Sum
{
 enum Value { N = solution4_Sum<n - 1>::N + n};
};
template <> struct solution4_Sum<1>
{
 enum Value { N = 1};
};