用C ++强大的功能 [英] Power very large number in C++

问题描述

有一点时间的人可以向我解释一下如何增加非常大的数字吗?我在这里不是在谈论一个现成的解决方案，而是关于如何实现该算法的唯一解释.理想情况下，它基于类std :: string.

Can someone with a bit of time, he could explain to me how intensify very large numbers? I'm not talking here about a ready solution, and the only explanation of how to implement the arithmetic. Ideally, it was based on the class std::string.

@edit

我阅读了一些有关移位位的信息，但示例仅以清单的形式出现，我想解释它的工作原理.

I read something about shifts bit, but examples were only in the form of a listing, and I want an explanation of how it works.

推荐答案

以下是我在需要时快速写的内容(不记得何时).它是:

Here is something I quickly wrote when I needed (do not remember when). It is:

1. 越野车；
2. 不完整；
3. 每个数组元素任意使用3位数字，但可以使用更多位；
4. 可以明显改善(欢迎任何形式的评论^^).

但是，我希望这会有所帮助.

However, I hope this will be somehow useful.

typedef long long int lli;

class BigInt
{
public: // Methods
    BigInt(lli s) : m_nbElements(100)
    {
        m_number.resize(m_nbElements);

        for (lli i=0; i < m_nbElements; ++i)
        {
            m_number[i] = s%1000;
            s /= 1000;
        }
    }

    BigInt(const std::string &str) : m_nbElements(100)
    {
        m_number.resize(m_nbElements);

        size_t sizeStr = str.size();
        int i = str.size() - 1;
        int thousands = 0;
        for (; i >= 2; i -= 3, ++thousands)
        {
            std::string subStr = str.substr(i-2, 3);
            unsigned int value;
            std::istringstream(subStr) >> value;
            m_number[thousands] = value;
        }

        // Handle the "first" 1 or 2 digits
        if (i >= 0)
        {
            std::string subStr = str.substr(0, i+1);
            unsigned int value;
            std::istringstream(subStr) >> value;
            m_number[thousands] = value;
        }
    }

    BigInt operator*(lli s)
    {
        lli temp, remainder = 0;
        for (lli i=0; i < m_nbElements; ++i)
        {
            temp = m_number[i] * s + remainder;
            m_number[i] = temp % 1000;
            remainder = temp / 1000;
        }

        return (*this);
    }

    BigInt operator/(lli s)
    {
        lli temp, remainder = 0;
        for (int i=m_nbElements-1; i >= 0; --i)
        {
            temp = (m_number[i] + remainder) / s;
            remainder = (m_number[i] % s)*1000;
            m_number[i] = temp;
        }

        return (*this);
    }

    BigInt operator-(BigInt s)
    {
        lli temp;
        for (unsigned int i=0; i < m_nbElements; ++i)
        {
            temp = m_number[i] - s.m_number[i];
            if (temp < 0)
            {
                --m_number[i+1];
                temp += 1000;
            }
            m_number[i] = temp;
        }

        return (*this);
    }

    BigInt operator+(BigInt s)
    {
        lli temp, remainder = 0;
        for (lli i=0; i < m_nbElements; ++i)
        {
            temp = m_number[i] + s.m_number[i] + remainder;
            m_number[i] = temp % 1000;
            remainder = temp / 1000;
        }

        return (*this);
    }

    std::string ToString()
    {
        std::string result = "";
        bool significantDigitsFound = false;
        for (int i=m_nbElements-1; i >= 0 ; --i)
        {
            if (!significantDigitsFound)
            {
                if (m_number[i] > 0)
                {
                    std::ostringstream ss;
                    ss << m_number[i];
                    result = ss.str();

                    significantDigitsFound = true;
                }
            }
            else
            {
                std::ostringstream ss;
                ss << std::setw(3) << std::setfill( '0' ) << m_number[i];
                result += ss.str();
            }
        }

        if (result == "")
        {
            result = "0";
        }

        return result;
    }

private: // Attributes
    int m_nbElements;
    std::vector<lli> m_number;
};

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