求1+2+...+n 【微软面试100题 第十二题】 - tractorman - 博客园


求1+2+...+n 【微软面试100题 第十二题】 - tractorman - 博客园

求1+2+...+n 【微软面试100题 第十二题】

题目要求:
  要求不能使用乘除法,for/while/if/else/switch/case等关键字以及条件判断语句(A?B:C)。
  参考资料:剑指offer第46题
题目分析:
  方法1:利用类的静态成员变量,定义一次之后该类的所有对象都共享该静态成员变量。再利用构造函数实现n次递加即可;
  方法2:利用函数指针;
  方法3:利用虚函数和动态联编(虚函数和动态联编介绍:http://blog.csdn.net/qlping2007/article/details/2177880).
http://www.cnblogs.com/lzmfywz/archive/2013/04/22/3036370.html
方法一:利用构造函数和静态数据成员
  1. class Temp  
  2. {  
  3. public:  
  4.     Temp()  
  5.     {  
  6.         ++N;  
  7.         Sum+=N;  
  8.     }  
  9.   
  10.     static void Reset()  
  11.     {  
  12.         N=0;  
  13.         Sum=0;  
  14.     }  
  15.   
  16.     static int GetSum()  
  17.     {  
  18.         return Sum;  
  19.     }  
  20. private:  
  21.     static int N;  
  22.     static int Sum;  
  23. };  
  24.   
  25. int Temp::N=0;  
  26. int Temp::Sum=0;  
  27.   
  28. int solution_Sum(int n)  
  29. {  
  30.     Temp::Reset();  
  31.   
  32.     Temp *a=new Temp[n];  
  33.     delete []a;  
  34.     a=0;  
  35.   
  36.     return Temp::GetSum();  



利用&&的短路特性
  1. int add_fun(int n, int &sum)  
  2. {  
  3.     n && add_fun(n-1, sum);  
  4.     return (sum+=n);  

int nFactorial(int n)2{
3    int num = 0;
4    (n > 0) && (num = n + nFactorial(n - 1));
5
6    return num;
7}

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