//利用类的构造

 class Temp{

 public:

     Temp() { ++N; sum += N; }

     static void Reset() { N = ; sum = ; }

     static unsigned int getRes() { return sum; }

 private:

     static unsigned int N, sum;//一定得是静态，否则每次创建是会重新赋值

 };

 unsigned int Temp::N = ; //一定得先初始化

 unsigned int Temp::sum = ;

 class Solution {

 public:

     int Sum_Solution(int n) {

         Temp::Reset();

         Temp *t = new Temp[n];

         delete[]t;

         t = nullptr;

         return Temp::getRes();

     }

 };

 //利用类的析构

 class A;

 A *Array[];

 class A{

 public:

     virtual unsigned int sum(unsigned int n){

         return ;

     }

 };

 class B :public A {

 public:

     virtual unsigned int sum(unsigned int n) {

         return Array[!!n]->sum(n - ) + n;

     }

 };

 int getSum(int n) {

     A a;

     B b;

     Array[] = &a;

     Array[] = &b;

     return Array[]->sum(n);

 }

 //利用函数指针

 typedef unsigned int(*fun)(unsigned int);

 unsigned int Solution3_Teminator(unsigned int n){

     return ;

 }

 unsigned int Sum_Solution3(unsigned int n){

     static fun f[] = { Solution3_Teminator, Sum_Solution3 };

     return n + f[!!n](n - );

 }

 // 利用模板

 template <unsigned int n> struct Sum_Solution4{

     enum Value { N = Sum_Solution4<n - >::N + n };

 };

 template <> struct Sum_Solution4<>{

     enum Value { N =  };

 };

 template <> struct Sum_Solution4<>{

     enum Value { N =  };

 };