// 面试题64：求1+2+…+n
// 题目：求1+2+…+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）。
#include <iostream>
// ====================方法一====================
//使用构造函数
class Temp
{
public:
Temp() { ++N; Sum += N; }
static void Reset() { N = ; Sum = ; }
static unsigned int GetSum() { return Sum; }
private:
static unsigned int N;
static unsigned int Sum;//静态成员，所有实例共享
};
unsigned int Temp::N = ;
unsigned int Temp::Sum = ;
unsigned int Sum_Solution1(unsigned int n)
{
Temp::Reset();
Temp *a = new Temp[n];//建立n次，实现sum加和
delete[]a;
a = NULL;
return Temp::GetSum();
}
// ====================方法二====================
//使用虚函数
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 Sum_Solution2(int n)
{
A a;
B b;
Array[] = &a;
Array[] = &b;
int value = Array[]->Sum(n);//当n大于0时，总是执行B类中的sum，直到n=0，!!n=0，然后变成了Array[0]->Sum(n)，即A类，注意Array设成全局变量
return value;
}
// ====================方法三====================
//使用函数指针
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 };//静态成员，第一次调用时候建立
return n + f[!!n](n - );
}
// ====================方法四====================
//使用模版类型
template <unsigned int n> struct Sum_Solution4
{
enum Value { N = Sum_Solution4<n - >::N + n };//Sum_Solution4<number>::N就是我们要的值
};
template <> struct Sum_Solution4<>
{
enum Value { N = };
};
template <> struct Sum_Solution4<>
{
enum Value { N = };
};
// ====================测试代码====================
void Test(int n, int expected)
{
printf("Test for %d begins:\n", n);
if (Sum_Solution1(n) == expected)
printf("Solution1 passed.\n");
else
printf("Solution1 failed.\n");
if (Sum_Solution2(n) == expected)
printf("Solution2 passed.\n");
else
printf("Solution2 failed.\n");
if (Sum_Solution3(n) == expected)
printf("Solution3 passed.\n");
else
printf("Solution3 failed.\n");
}
void Test1()
{
const unsigned int number = ;
int expected = ;
Test(number, expected);
if (Sum_Solution4<number>::N == expected)
printf("Solution4 passed.\n");
else
printf("Solution4 failed.\n");
}
void Test2()
{
const unsigned int number = ;
int expected = ;
Test(number, expected);
if (Sum_Solution4<number>::N == expected)
printf("Solution4 passed.\n");
else
printf("Solution4 failed.\n");
}
void Test3()
{
const unsigned int number = ;
int expected = ;
Test(number, expected);
if (Sum_Solution4<number>::N == expected)
printf("Solution4 passed.\n");
else
printf("Solution4 failed.\n");
}
void Test4()
{
const unsigned int number = ;
int expected = ;
Test(number, expected);
if (Sum_Solution4<number>::N == expected)
printf("Solution4 passed.\n");
else
printf("Solution4 failed.\n");
}
int main(int argc, char* argv[])
{
Test1();
Test2();
Test3();
Test4();
system("pause");
return ;
}