题解:[P1009 阶乘之和]

- [P1009 阶乘之和](https://www.luogu.com.cn/problem/P1009)

QAQ，刚开始看完题直接立刻按照题目阶乘相加写出了程序，数据使用int类型处理，4个测试点只通过两个。

感觉应该是int型数据不够大，存不下结果，然后换成了long long测试一遍还是不行，又换成了unsigned long long，还是不够大，

下载了第三个测试点看了一下，发现是22的阶乘，结果是1177652997443428940313，￣□￣｜｜。。。。。。。。。。

//这个不行
#include<iostream>
#include<cmath>
#include<iomanip>
#include <stdio.h>
#include <math.h>
using namespace std;
unsigned long long jc(unsigned long long n);
int main()
{
    unsigned long long n,s=1,s2=0;
    cin>>n;
    for(unsigned long long i = 1; i<=n; i++)
        s2+=jc(i);
    cout<<s2;
    return 0;
}

unsigned long long jc(unsigned long long n)
{
    unsigned long long s = 1;
    for(unsigned long long i = 1; i<=n; i++)
        s*=i;
    return s;
}

发现题目提示用高精度计算，花了大半天用数组写了一个超长数据加法乘法器终于全部ac,

#include<iostream>
#include<sstream>
using namespace std;
class Operator
{
public:
    string input;
    int data[100];
    int length;
    void init();
    Operator(string s);
    void setdata(string s);
    void printdata();
    int adder(Operator ope);
    int subtractor(Operator ope);
    int multiplier(Operator ope,int n);
    int divider(Operator ope);
};

Operator::Operator(string s)
{
    if(s=="0")
    {
        init();
    }
    else
    {
        for(int i = 0; i<100; i++)
        {
            data[i]=0;
        }
        input = s;
        length = s.length();
        stringstream ss;
        for(int i = 0; i<length; i++)
        {
            ss<<s[i];
            ss>>data[length-i-1];
            ss.clear();
        }
    }
}

void Operator::init()
{
    for(int i = 0; i<100; i++)
    {
        data[i]=0;
    }
    input = "";
    this->length = 0;
}

void Operator::printdata()
{
    cout<<"data = ";
    for(int i = length-1; i>=0; i--)
    {
        cout<<data[i];
    }
    if(length==0)
        cout<<"0";
    cout<<"  string ="<<input;
    cout<<"  length = "<<length;
    cout<<endl;
}

void Operator::setdata(string s)
{
    input = s;
    length = s.length();
    stringstream ss;
    for(int i = 0; i<length; i++)
    {
        ss<<input[i];
        ss>>data[length-i-1];
        ss.clear();
    }
}

int Operator::adder(Operator ope)
{
    int add_bit = 0;
    this->length = max(this->length,ope.length);
    for(int i = 0; i<max(this->length,ope.length); i++)
    {
        int d = this->data[i]+ope.data[i];
        if(add_bit!=0)
            d+=1;
        if(d>9)
            add_bit = 1;
        else
            add_bit = 0;
        this->data[i] = d%10;
    }
    if(add_bit==1)
    {
        this->data[length]=1;
        this->length = length+1;
    }
    stringstream ss;
    input.resize(this->length);
    for(int i = 0; i<this->length; i++)
    {
        ss<<data[this->length-i-1];
        ss>>this->input[i];
        ss.clear();
    }
    return 1;
}

int Operator::multiplier(Operator ope,int n)
{
    Operator ope_copy(ope.input);
    for(int i = 1; i<n; i++)
    {
        this->adder(ope_copy);
    }

    return 1;
}

int Operator::subtractor(Operator ope)
{
    return 0;
}

int Operator::divider(Operator ope)
{
    return 0;
}

int main()
{
    int n;
    cin>>n;

    Operator sum_factorial("0");
    for(int i = 1; i<=n; i++)
    {
        Operator factorial("1");
        for(int j = 1; j<=i; j++)
        {
            factorial.multiplier(factorial,j);

        }

        sum_factorial.adder(factorial);
    }

    cout<<sum_factorial.input;


    return 0;
}

真不容易，想刷点大水题。。。。。。。。。。