剑指offer——面试题46：求1+2+...+n的多种解法

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
;
delete []a;
a = NULL;

return Temp::GetSum();
}





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;
}



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);
}



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};
};

template <> struct Sum_Solution4<0>
{
enum Value { N = 0};
};