플리나를 위하여

long long int Problem010(int number)
{
	long long int ret = 0;
	int* numArr = new int[number + 1];
	for (int i = 2; i <= number; i++)
	{
		numArr[i] = -1;
	}
	for (int i = 2; i <= number; i++)
	{
		if (numArr[i] == -1)
		{
			ret += i;
			for (int j = i * 2; j <= number; j += i)
			{
				numArr[j] = 0;
			}
		}
	}
	delete[] numArr;
	return ret;
}

int Problem009(int number)
{
	int ret = -1;
	bool escape = false;
	for (int a = 1; a < number / 3; a++)
	{
		for (int b = a + 1; b < number - a; b++)
		{
			int c = number - a - b;
			if (b >= c)
			{
				break;
			}
			if (a * a + b * b == c * c)
			{
				ret = a * b * c;
				escape = true;
				break;
			}
		}
		if (escape)
		{
			break;
		}
	}
	return ret;
}

// 본문에 있는 숫자 배열은 "Project_Euler_008.txt"에 저장
long long int Problem008(int digitScope)
{
	char* numbers = new char[1000];
	char* read = new char[51];
	std::ifstream file("Project_Euler_008.txt");
	for(char i = 0; i < 20; i++)
	{
		file.getline(read, 51);
		for (char j = 0; j < 50; j++)
		{
			numbers[50 * i + j] = read[j] - '0';
		}
	}
	delete[] read;
	file.close();

	long long int ret = 0;
	for (int i = 0; i < 1000 - digitScope; i++)
	{
		long long int multiple = 1;
		for (int j = 0; j < digitScope; j++)
		{
			if (numbers[i + j] == 0)
			{
				i = i + j;
				break;
			}
			multiple *= numbers[i + j];
		}
		if (multiple > ret)
		{
			ret = multiple;
		}
	}
	delete[] numbers;
	return ret;
}

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;
}