剑指offer——求1+2+3+....+n!

题目描述：求1+2+3+...+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）。

class Solution {
public:
    //递归方法
	int Sum_Solution(int n) {
		int ans = n;
		ans && (ans += Sum_Solution(n - 1));
		return ans;
	}
        //非递归方法
        int Sum_Solution2(int n) {
            bool a[n][n+1];
            return sizeof(a)>>1;
        }
};

 

//比较新颖的想法
typedef int (*func)( int );
class Solution {
public:
    static int Solution1(int n )
        { return 0;}
 
 
static int Sum_Solution(int n) {
     
     
        static func f[2] = {Solution1,Sum_Solution};
        return n+f[!!n](n-1);
 
 
    }
     
};

class Tmp
{
public:
    Tmp()
    {
        ++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 Tmp::N = 0;
unsigned int Tmp::Sum = 0;
class Solution
{
public:
    friend class Tmp;
public:
    int Sum_Solution(int n)
    {
        Tmp::Reset();
        Tmp *a = new Tmp[n];
        delete[] a;
        a = NULL;
        return Tmp::GetSum();
    }
 
};