大整数模板（c++)—算法竞赛入门

#include <map>
#include <set>
#include <cmath>
#include <queue>
#include <stack>
#include <vector>
#include <bitset>
#include <string>
#include <string.h>
#include <limits.h>
#include <stdio.h>
#include <iostream>
#include <algorithm>
using namespace std;
class BigNum;
istream& operator>>(istream&,  BigNum&);
ostream& operator<<(ostream&,  BigNum&);
#define MAXN 9999
#define MAXSIZE 100000
#define DLEN 4
class BigNum
{
public:
int a[MAXSIZE];
int len;
public:
BigNum(){len = 1;memset(a,0,sizeof(a));}
BigNum(const int);
BigNum(const char*);
BigNum(const BigNum &);
BigNum &operator=(const BigNum &);
friend istream& operator>>(istream&,  BigNum&);
friend ostream& operator<<(ostream&,  BigNum&);
BigNum operator+(const BigNum &) const;
BigNum operator-(const BigNum &) const;
BigNum operator*(const BigNum &) const;
BigNum operator/(const int  &) const;
BigNum operator^(const int  &) const;
int    operator%(const int  &) const;
bool   operator>(const BigNum & T)const;
bool   operator==(const BigNum & T)const;
bool   operator==(const int & t)const;
bool   operator>(const int & t)const;
};
istream& operator>>(istream & in,  BigNum & b)
{
char ch[MAXSIZE*4];
int i = -1;
in>>ch;
int l=strlen(ch);
int count=0,sum=0;
for (i=l-1;i>=0;)
{
sum = 0;
int t=1;
for (int j=0;j<4&&i>=0;j++,i--,t*=10)
{
sum+=(ch[i]-'0')*t;
}
b.a[count]=sum;
count++;
}
b.len =count++;
return in;

}
ostream& operator<<(ostream& out,  BigNum& b)
{
int i;
cout << b.a[b.len - 1];
for (i = b.len - 2 ; i >= 0 ; i--)
{
cout.width(DLEN);
cout.fill('0');
cout << b.a[i];
}
return out;
}
BigNum::BigNum(const int b)
{
int c,d = b;
len = 0;
memset(a,0,sizeof(a));
while (d > MAXN)
{
c = d - (d / (MAXN + 1)) * (MAXN + 1);
d = d / (MAXN + 1);  a[len++] = c;
}
a[len++] = d;
}
BigNum::BigNum(const char*s)
{
int t,k,index,l;
memset(a,0,sizeof(a));
l=strlen(s);
len=l/DLEN;
if (l%DLEN)len++;
index=0;
for (int i=l-1;i>=0;i-=DLEN)
{
t=0;k=i-DLEN+1;
if (k<0)k=0;
for (int j=k;j<=i;j++)
t=t*10+s[j]-'0';
a[index++]=t;
}
}
BigNum::BigNum(const BigNum & T) : len(T.len)
{
int i;
memset(a,0,sizeof(a));
for (i = 0 ; i < len ; i++)  a[i] = T.a[i];
}
BigNum & BigNum::operator=(const BigNum & n)
{
len = n.len;
memset(a,0,sizeof(a));
for (int i = 0 ; i < len ; i++)
a[i] = n.a[i];
return *this;
}
BigNum BigNum::operator+(const BigNum & T) const
{
BigNum t(*this);
int i,big;
big = T.len > len ? T.len : len;
for (i = 0 ; i < big ; i++)
{
t.a[i] +=T.a[i];
if (t.a[i] > MAXN)
{
t.a[i + 1]++;
t.a[i] -=MAXN+1;
}
}
if (t.a[big] != 0) t.len = big + 1;
else t.len = big;
return t;
}
BigNum BigNum::operator-(const BigNum & T) const
{
int i,j,big;
bool flag;
BigNum t1,t2;
if (*this>T)
{
t1=*this;
t2=T;
flag=0;
}
else
{
t1=T;
t2=*this;
flag=1;
}
big=t1.len;
for (i = 0 ; i < big ; i++)
{
if (t1.a[i] < t2.a[i])
{
j = i + 1;
while (t1.a[j] == 0) j++;
t1.a[j--]--;
while (j > i) t1.a[j--] += MAXN;
t1.a[i] += MAXN + 1 - t2.a[i];
}
else t1.a[i] -= t2.a[i];
}
t1.len = big;
while (t1.a[len - 1] == 0 && t1.len > 1)
{
t1.len--;
big--;
}
if (flag)t1.a[big-1]=0-t1.a[big-1];
return t1;
}
BigNum BigNum::operator*(const BigNum & T) const
{
BigNum ret;
int i,j,up;
int temp,temp1;
for (i = 0 ; i < len ; i++)
{
up = 0;
for (j = 0 ; j < T.len ; j++)
{
temp = a[i] * T.a[j] + ret.a[i + j] + up;
if (temp > MAXN)
{
temp1 = temp - temp / (MAXN + 1) * (MAXN + 1);
up = temp / (MAXN + 1);
ret.a[i + j] = temp1;
}
else
{
up = 0;
ret.a[i + j] = temp;
}
}
if (up != 0)
ret.a[i + j] = up;
}
ret.len = i + j;
while (ret.a[ret.len - 1] == 0 && ret.len > 1) ret.len--;
return ret;
}
BigNum BigNum::operator/(const int & b) const
{
BigNum ret;
int i,down = 0;
for (i = len - 1 ; i >= 0 ; i--)
{
ret.a[i] = (a[i] + down * (MAXN + 1)) / b;
down = a[i] + down * (MAXN + 1) - ret.a[i] * b;
}
ret.len = len;
while (ret.a[ret.len - 1] == 0 && ret.len > 1) ret.len--;
return ret;
}
int BigNum::operator %(const int & b) const
{
int i,d=0;
for (i = len-1; i>=0; i--)
{
d = ((d * (MAXN+1))% b + a[i])% b;
}
return d;
}
BigNum BigNum::operator^(const int & n) const
{
BigNum t,ret(1);
int i;
if (n<0)exit(-1);
if (n==0)return 1;
if (n==1)return *this;
int m=n;
while (m>1)
{
t=*this;
for ( i=1;i<<1<=m;i<<=1)
{
t=t*t;
}
m-=i;
ret=ret*t;
if (m==1)ret=ret*(*this);
}
return ret;
}
bool BigNum::operator>(const BigNum & T) const
{
int ln;
if (len > T.len) return true;
else if (len == T.len)
{
ln = len - 1;
while (a[ln] == T.a[ln] && ln >= 0) ln--;
if (ln >= 0 && a[ln] > T.a[ln]) return true;
else return false;
}
else return false;
}

bool BigNum::operator==(const BigNum & T) const
{
int ln;
if (len != T.len) return false;
else
{
ln = len - 1;
while (a[ln] == T.a[ln] && ln-- );
if (ln < 0) return true;
else return false;
}
}

bool BigNum::operator >(const int & t) const
{
BigNum b(t);
return *this>b;
}

bool BigNum::operator==(const int & t) const
{
BigNum b(t);
return *this==b;
}
// 求n的阶乘
int main()
{
int n,i;
BigNum S;
cin>>n;
S=1;
for(i=1;i<=n;i++)
S=S*i;
cout<<S<<endl;
return 0;
}