高精度，求条

P1009 [NOIP1998 普及组] 阶乘之和

little_q_exist @ 2024-10-23 20:33:57

样例都妹过（泪

#include<iostream>
#include<cstring>
using namespace std;
int a[52],b[52],c[102],d[52],f[102];
int len_a = 0,len_b = 1,len_c = 1,len_d = 1;
int main(){
    int n;
    b[0] = 1;
    cin>>n;
    for (int i = 1;i<=n;i++)
    {
        int p = i;
        while (p>0) //采用在i-1的结果上累乘i 
        {
            a[len_a] = p%10;//把i输入a数组 
            p /= 10;
            len_a ++;
        }
        for (int i = 0;i<len_a;i++)
        {
            for (int j = 0;j<len_b;j++)
            {
                c[i+j] += a[i]*b[j];//高精乘 
            }
        }
        while (c[len_c]) len_c ++;
        for (int i = 0;i<len_c;i++)
        {
            if (c[i] > 9)//c数组中存结果 
            {
                c[i+1] += c[i]/10;
                c[i] %= 10;
            }
        }
        while (c[len_c]) len_c ++;
        len_b = len_c;//结果丢到b数组 
        for (int i = 0;i<len_b;i++)
        {
            b[i] = c[i];
        }
        //同时进行高精加法
        for (int i = 0;i<len_c;i++)
        {
            d[i] += c[i];
        }
        while (d[len_d]) len_d ++;
        for (int i = 0;i<len_d;i++)
        {
            if (d[i] > 9)
            {
                d[i+1] += d[i]/10;
                d[i] %= 10;
            }
        }
        while (d[len_d]) len_d ++;
    }
    for (int i = len_d - 1;i>=0;i--)
    {
        cout<<d[i];
    }
    cout<<endl;
    return 0;
}

by 佳睿2012 @ 2024-10-23 20:41:11

应是c[i+j+1]=a[i] * b[j]

by geyuqian @ 2024-11-04 19:05:59

可以看看我用c写的

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#define MAX_BIT 2000
//大数加法
void num_add(int* sum, int* num)
{
    int i = 0;
    int flag = 0;
    for (i = 0; i < MAX_BIT; i++) {
        sum[i] += num[i] + flag;
        flag = sum[i] / 10;
        sum[i] %= 10;
    }
}

//大数乘法
void num_multiply(int* num, int x)
{
    int flag = 0;
    int i = 0;
    for (i = 0; i < MAX_BIT; i++) {
        num[i] =num[i]* x + flag;
        flag = num[i] / 10;
        num[i] %= 10;
    }
}

//计算阶乘
void result(int n)
{
    int i = 0;
    int tmp[MAX_BIT];
    int ret[MAX_BIT];
    memset(ret, 0, sizeof(ret));
    memset(tmp, 0,sizeof(tmp));
    tmp[0] = 1;
    for (i = 1;i <= n; i++) {
        num_multiply(tmp, i);
        num_add(ret, tmp);
    }
    for (i = MAX_BIT - 1; i >= 0; i--) {
        if (ret[i] != 0) {
            break;
        }
    }
    for (; i >=0 ; i--) {
        printf("%d", ret[i]);
    }
}
int main()
{
    int input = 0;
    scanf("%d", &input);
    result(input);
    return 0;
}