플리나를 위하여

long long int Problem007(unsigned int number)
{
	long long int ret;
	unsigned int count = 0;
	for (int i = 2; true; i++)
	{
		if (IsPrime(i))
		{
			ret = i; 
			count++;
		}
		if (count == number)
		{
			break;
		}
	}
	return ret;
}
bool IsPrime(int number)
{
	bool ret = true;
	for (int i = 2; i * i <= number; i++)
	{
		if (number % i == 0)
		{
			ret = false;
			break;
		}
	}
	return ret;
}

long long int Problem006(unsigned int number)
{
	long long int sum = SumUpToScope(number);
	long long int Squares = 0;
	for (unsigned int i = 1; i <= number; i++)
	{
		Squares += i * i;
	}
	return sum * sum - Squares;
}

int SumUpToScope(int scope)
{
	return ((1 + scope) * scope) / 2;
}

long long int Problem005(int number)
{
	long long int ret = 1;
	long long int factor;
	for (int i = 2; i <= number; i++)
	{
		factor = 1;
		if (IsPrime(i))
		{
			while (factor <= number)
			{
				factor *= i;
			}
			factor /= i;
			ret *= factor;
		}
	}
	return ret;
}

bool IsPrime(int number)
{
	bool ret = true;
	for (int i = 2; i * i <= number; i++)
	{
		if (number % i == 0)
		{
			ret = false;
			break;
		}
	}
	return ret;
}

int Problem004(int digit)
{
	int ret = -1;
	int start = 1;
	for (int i = 1; i < digit; i++)
	{
		start *= 10;
	}
	int end = start * 10;
	for (int i = start; i < end; i++)
	{
		for (int j = start; j < end; j++)
		{
			if (SymmetryChecker(i * j) && ret < i * j)
			{
				ret = i * j;
			}
		}
	}
	return ret;
}

int GetDigit(int number)
{
	if (number == 0)
	{
		return 0;
	}
	if (number < 0)
	{
		number *= -1;
	}
	int ret = 1;
	while (true)
	{
		number /= 10;
		if (number == 0)
		{
			break;
		}
		ret++;
	}
	return ret;
}

bool SymmetryChecker(int number)
{
	int digit = GetDigit(number);
	char* numArr = new char[digit];
	for (int i = 0; i < digit; i++)
	{
		numArr[i] = number % 10;
		number /= 10;
	}

	bool ret = true;
	for (int i = 0; i < digit / 2; i++)
	{
		if (numArr[i] != numArr[digit - i - 1])
		{
			ret = false;
			break;
		}
	}
	delete[] numArr;
	return ret;
}

long long int Problem003(long long int number)
{
	long long int ret = number;
	long long int i = 1;
	while (i * i <= number)
	{
		i++;
		if (number % i == 0)
		{
			ret = i;
			number /= i;
			i = 1;
			if (number == 1)
			{
				break;
			}
		}
	}
	return ret;
}

int Problem002(int first, int second, int scope)
{
	int ret = 0;
	int third = first + second;

	if (first % 2 == 0)
	{
		ret += first;
	}
	if (second % 2 == 0)
	{
		ret += second;
	}

	while (true)
	{
		if (third > scope)
		{
			break;
		}
		if (third % 2 == 0)
		{
			ret += third;
		}
		first = second;
		second = third;
		third = first + second;
	}
	return ret;
}

int num1 = 3, int num2 = 5, int scope = 1000

// 일반적인 구현
int Problem001(int num1, int num2, int scope)
{
	int ret = 0;
	for (int i = 1; i < scope; i++)
	{
		if (i%num1 == 0 || i % num2 == 0)
		{
			ret += i;
		}
	}
	return ret;
}

// 수학 공식을 통한 구현
int Problem001(int num1, int num2, int scope)
{
	scope--;
	return sumUpToScope(num1, scope) + sumUpToScope(num2, scope) - sumUpToScope(num1 * num2, scope);
}

int sumUpToScope(int num, int scope)
{
	return (((1 + (scope / num)) * (scope / num)) / 2) * num;
}