模板——BigInteger

#include <iostream>
#include <cstring>
#include <string>
#include <vector>
#include <set>
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;


struct Bign
{
    static const int BASE=100000000;
    static const int WIDTH=8;
    vector<int>s;

    Bign(LL n=0){*this=n;}
    Bign(const string& str){*this=str;}
    Bign operator =(LL n)
    {
        s.clear();
        do
        {
            s.push_back(n%BASE);
            n/=BASE;
        }while(n>0);
        return *this;
    }
    Bign operator =(const string& str)
    {
        s.clear();
        int x,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;
    }
    Bign operator +(const Bign& b)const
    {
        int len1=s.size(),len2=b.s.size();
        int len=max(len1,len2);
        int ans=0;
        Bign c;c.s.clear();
        for(int i=0;i<len||ans!=0;i++)
        {
            if(i<len1) ans+=s[i];
            if(i<len2) ans+=b.s[i];
            c.s.push_back(ans%BASE);
            ans/=BASE;
        }
        return c;
    }
    Bign operator -(const Bign& b)const
    {

        int len1=s.size(),len2=b.s.size();
        Bign c;c.s.clear();
        int ans=0,t=0;
        for(int i=0;i<len1;i++)
        {
            if(i<len2) ans=s[i]-b.s[i]+t;
            else ans=s[i]+t;
            if(ans<0)
            {
                ans+=BASE;t=-1;
            }
            else t=0;
            if(ans>0)c.s.push_back(ans);
        }
        return c;
    }
    Bign operator *(const Bign& b)const
    {
        Bign c;
        int len1=s.size(),len2=b.s.size();
        for(int i=0;i<len2;i++)
        {
            for(int j=0;j<len1;j++)
            {
                Bign ans=(LL)b.s[i]*s[j];
                for(int k=0;k<i+j;k++)
                ans.s.insert(ans.s.begin(),0);
                c=c+ans;
            }
        }
        return c;
    }

    bool operator <(const Bign& 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 Bign& b)const
    {
        if(s.size()!=b.s.size()) return false;
        for(int i=s.size()-1;i>=0;i--)
            if(s[i]!=b.s[i]) return false;
        return true;
    }
};
ostream& operator <<(ostream& out,const Bign& a)
{
    out<<a.s.back();
    char buf[10];
    int len=a.s.size();
    for(int i=len-2;i>=0;i--)
    {
        sprintf(buf,"%08d",a.s[i]);
        out<<buf;
    }
    return out;
}
LL BtoL(const Bign& a)
{
    LL c;
    char buf[10];
    string ss="";
    int len=a.s.size();
    sprintf(buf,"%d",a.s.back());ss+=(string)buf;
    for(int i=len-2;i>=0;i--)
    {
        sprintf(buf,"%08d",a.s[i]);
        ss+=(string)buf;
    }
    sscanf(ss.c_str(),"%lld",&c);
    return c;
}
istream& operator >>(istream& in,Bign& a)
{
    string s;
    in>>s;
    a=s;
    return in;
}