hdu1042

向牛人看起！http://acm.hdu.edu.cn/showproblem.php?pid=1042

摘自：http://www.cnblogs.com/phinecos/archive/2009/10/06/1578411.html

#include<iostream>

#include<stdio.h>

#include<string>

#include<iomanip>

#include<algorithm>

using namespace std;

#include "time.h"



const int MAX_GROUPS = 20000;//最多2万组，每组最多4位整数，即最多可容纳8万位整数

const int MAXN = 9999;//每组的上限值

const int GROUP_LEN = 4;//每组的最大长度



class BigInteger

{

private:

    int data[MAX_GROUPS];

    int len;

    void init()

    {

        memset(data,0,sizeof(data));

    }

public:

    BigInteger()

    {

        init();

        len = 0;

    }

    BigInteger(const int b);

    BigInteger(const BigInteger &);



    bool operator > (const BigInteger&)const;

    BigInteger & operator=(const BigInteger &);

    BigInteger & add(const BigInteger &);

    BigInteger & sub(const BigInteger &);

    BigInteger operator+(const BigInteger &) const;

    BigInteger operator-(const BigInteger &) const;

    BigInteger operator*(const BigInteger &) const;

    BigInteger operator/(const int &) const;

    void print();

};

BigInteger::BigInteger(const int num)

{

    int res,tmp = num;

    len = 0;

    init();

    while(tmp > MAXN)

    {

        res = tmp - tmp / (MAXN + 1) * (MAXN + 1);

        tmp = tmp / (MAXN + 1);

        data[len++] = res;

    }

    data[len++] = tmp;

}

BigInteger::BigInteger(const BigInteger & rhs) : len(rhs.len)

{

    int i;

    init();

    for(i = 0 ; i < len ; i++)

    {

        data[i] = rhs.data[i];

    }

}

bool BigInteger::operator > (const BigInteger &rhs)const

{

    int ln;

    if(len > rhs.len)

    {

        return true;

    }

    else if(len < rhs.len)

    {

        return false;

    }

    else if(len == rhs.len)

    {

        ln = len - 1;

        while(data[ln] == rhs.data[ln] && ln >= 0) 

        {

            ln--;

        }

        if(ln >= 0 && data[ln] > rhs.data[ln]) 

        {

            return true;

        }

        else 

        {

            return false;

        }

    }



}



BigInteger & BigInteger::operator = (const BigInteger &rhs)

{

    init();

    len = rhs.len;

    for(int i = 0 ; i < len ; i++)

    {

        data[i] = rhs.data[i];

    }

    return *this;

}

BigInteger& BigInteger::add(const BigInteger &rhs)

{

    int i,nLen;



    nLen = rhs.len > len ? rhs.len : len;

    for(i = 0 ; i < nLen ; i++)

    {

        data[i] = data[i] + rhs.data[i];

        if(data[i] > MAXN)

        {

            data[i + 1]++;

            data[i] = data[i] - MAXN - 1;

        }

    }

    if(data[nLen] != 0) 

    {

        len = nLen + 1;

    }

    else 

    {

        len = nLen;

    }



    return *this;

}

BigInteger & BigInteger::sub(const BigInteger &rhs)

{

    int i,j,nLen;

    if (len > rhs.len)

    {

        for(i = 0 ; i < nLen ; i++)

        {

            if(data[i] < rhs.data[i])

            {

                j = i + 1;

                while(data[j] == 0) j++;

                data[j]--;

                --j;

                while(j > i)

                {

                    data[j] += MAXN;

                    --j;

                }

                data[i] = data[i] + MAXN + 1 - rhs.data[i];

            }

            else 

            {

                data[i] -= rhs.data[i];

            }

        }

        len = nLen;

        while(data[len - 1] == 0 && len > 1) 

        {

            --len;    

        }

    }

    else if (len == rhs.len)

    {

        for(i = 0 ; i < len ; i++)

        {

            data[i] -= rhs.data[i];

        }

        while(data[len - 1] == 0 && len > 1) 

        {

            --len;    

        }

    }

    return *this;

}

BigInteger BigInteger::operator+(const BigInteger & n) const 

{

    BigInteger a = *this;

    a.add(n);

    return a;

}

BigInteger BigInteger::operator-(const BigInteger & T) const

{

    BigInteger b = *this;

    b.sub(T);

    return b;

}

BigInteger BigInteger::operator * (const BigInteger &rhs) const

{

    BigInteger result;

    int i,j,up;

    int temp,temp1;



    for(i = 0; i < len; i++)

    {

        up = 0;

        for(j = 0; j < rhs.len; j++)

        {

            temp = data[i] * rhs.data[j] + result.data[i + j] + up;

            if(temp > MAXN)

            {

                temp1 = temp - temp / (MAXN + 1) * (MAXN + 1);

                up = temp / (MAXN + 1);

                result.data[i + j] = temp1;

            }

            else 

            {

                up = 0;

                result.data[i + j] = temp;

            }

        }

        if(up != 0)

        {

            result.data[i + j] = up;

        }

    }

    result.len = i + j;

    while(result.data[result.len - 1] == 0 && result.len > 1) result.len--;

    return result;

}

BigInteger BigInteger::operator/(const int & b) const

{

    BigInteger ret;

    int i,down = 0;



    for(i = len - 1 ; i >= 0 ; i--)

    {

        ret.data[i] = (data[i] + down * (MAXN + 1)) / b;

        down = data[i] + down * (MAXN + 1) - ret.data[i] * b;

    }

    ret.len = len;

    while(ret.data[ret.len - 1] == 0) ret.len--;

    return ret;

}

void BigInteger::print()

{

    int i;



    cout << data[len - 1];

    for(i = len - 2 ; i >= 0 ; i--)

    {

        cout.width(GROUP_LEN);

        cout.fill('0');

        cout << data[i];

    }

    cout << endl;

}

int main()

{  

    clock_t   start,   finish;   

    double     duration;   

    int i,n;

    BigInteger result,num;

    scanf("%d",&n);

    start   =   clock();    

    result = BigInteger(1);

    for(i = 2;i <= n; ++i)

    {

        num = BigInteger(i);

        result = result * num;

    }

    result.print();

    finish   =   clock();   

    duration   =   (double)(finish   -   start)   /   CLOCKS_PER_SEC;  

    printf(   "%f   seconds\n",   duration   );   

    return 0;

}