大数阶乘

源代码

#include <cstring>
#include <cstdio>
int a[20000];
int main()
{
    int m, ans, carray,num;//m为输入数，ans为当前数与乘积数的每一位的乘积，carray为进位数
    //比如ans + carray = 5015，那么更新乘积的当前位为5，carray更新为501（右移了一位），num为需要多少位数组
    while (scanf("%d",&m)!=EOF)
    {
        memset(a,0,20000);
        a[0] = 1;
        carray = 0;
        num = 1;
        for (int j = 1; j <= m; j++)
        {
            for (int i = 0; i < num; i++)
            {
                ans = a[i] * j;
                a[i] = (ans + carray) % 10;
                carray = (ans + carray) / 10;
                if (carray && num < i + 2)
                    num = i + 2;
            }
        }
        int i = 20000;
        while (!a[--i]);
        for (; i >= 0; i--)
        {
            printf("%d",a[i]);
        }
        printf("\n");
    }
    return 0;
}

最优源代码

#include<stdio.h>
#include<string.h>
const int maxn=20000;
int a[maxn];
int main()
{
    int n,i,j,s,c;
    scanf("%d",&n);
    memset(a,0,sizeof(a));
    a[0]=1;
    for(i=2;i<=n;i++)
    {c=0;
    for(j=0;j<=maxn;j++)
    {
    s=a[j]*i+c;
    a[j]=s%10;
    c=s/10;
    }
    }
    for(j=maxn;j>=0;j--) if(a[j]) break;
    for(i=j;i>=0;i--) printf("%d",a[i]);
    printf("\n");
    return 0;
}