Cattle off network - to prove safety office- seeking 1 + 2 + 2 + ... + n

Title: seeking 1 + 2 + 3 + ... + n, requires multiplication and division can not be used, for, while, if, else , switch, case and keywords such as conditional statement (A B:? C).
Solution one:
idea: recursive summation.

class Solution {
public:
    int Sum_Solution(int n) {
        int sum =n;
        sum &&(sum+=Sum_Solution(n-1));
        return sum;
    }
};

Solution two:
thinking: using the constructor solved. We first define a class, then create instances of the n type, then the constructor will be called n times, we can accumulate code into the constructor function.

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;
class Solution {
public:
    int Sum_Solution(int n) {
        Temp::Reset();
	Temp* a = new Temp[n];
	delete[]a;
	a = nullptr;
	return Temp::GetSum();
    }
};

Solution three:
thinking: the use of virtual functions to solve.

class A;
A *Array[2];
class A
{
public:
	virtual unsigned int Sum(unsigned int n)
	{
		return 0;
	}
};
class B :public A
{
public:
	 unsigned int Sum(unsigned int n)
	{
		return Array[!!n]->Sum(n - 1) + n;
	}
};
class Solution {
public:
    int Sum_Solution(int n) {
        A a;
	B b;
	Array[0] = &a;
	Array[1] = &b;
	int value = Array[1]->Sum(n);
	return value;
    }
};