刘汝佳 BigInteger 大数模板

struct BigInteger
{
    static const int BASE = 100000000;
    static const int WIDTH = 8;
    vector<int> s;
    BigInteger(long long num = 0)
    {
        *this = num;
    }
    BigInteger operator=(long long num)
    {
        s.clear();
        do {
            s.push_back(num%BASE);
            num /= BASE;
        } while (num > 0);
        return *this;
    }
    BigInteger operator=(const string& str)
    {
        s.clear();
        int x;
        int len=(str.length() - 1)/WIDTH + 1;
        for (int i = 0;i < len;i++)
        {
            int end = str.length() - i*WIDTH;
            int start = max(0, end - WIDTH);
            sscanf(str.substr(start, end - start).c_str(), "%d", &x);
            s.push_back(x);
        }
        return *this;
    }
    BigInteger operator+(const BigInteger& b) const {
        BigInteger c;
        c.s.clear();
        for (int i = 0,g = 0;;i++)
        {
            if (g == 0 && i >= s.size() && i >= b.s.size())
                break;
            int x = g;
            if (i < s.size())
                x += s[i];
            if (i < b.s.size())
                x += b.s[i];
            c.s.push_back(x%BASE);
            g = x / BASE;
        }
        return c;
    }
    BigInteger operator +=(const BigInteger& b)
    {
        *this = *this + b;
        return *this;
    }
    bool operator<(const BigInteger& b)const
    {
        if (s.size() != b.s.size())
            return s.size() < b.s.size();
        for (int i = s.size() - 1;i >= 0;i--)
            if (s[i] != b.s[i])
                return s[i] < b.s[i];
        return false;
    }
    bool operator >(const BigInteger& b)const { return b < *this; }
    bool operator <=(const BigInteger& b)const { return !(b < *this); }
    bool operator >=(const BigInteger& b)const { return !(*this < b); }
    bool operator !=(const BigInteger& b)const { return b < *this || *this < b; }
    bool operator ==(const BigInteger& b)const { return !(b < *this) && !(*this < b); }
};


ostream& operator << (ostream &out, const BigInteger& x)
{
    out << x.s.back();
    for (int i = x.s.size() - 2;i >= 0;i--)
    {
        char buf[20];
        sprintf(buf, "%08d", x.s[i]);
        for (int j = 0;j < strlen(buf);j++)
            out << buf[j];
    }
    return out;
}
istream& operator >> (istream &in, BigInteger& x)
{
    string s;
    if (!(in >> s))
        return in;
    x = s;
    return in;
}