TOJ-1304 Factovisors

The factorial function, n! is defined thus for n a non-negative integer:

   0! = 1
   n! = n * (n-1)!   (n > 0)

We say that a divides b if there exists an integer k such that

   k*a = b

The input to your program consists of several lines, each containing two non-negative integers, n and m, both less than 2³¹. For each input line, output a line stating whether or not m divides n!, in the format shown below.

Sample Input

6 9
6 27
20 10000
20 100000
1000 1009

Sample Output

9 divides 6!
27 does not divide 6!
10000 divides 20!
100000 does not divide 20!
1009 does not divide 1000!


Source: Waterloo Local Contest Jan. 31, 1999

因式分解m，看n！能否分解出这些因式。

#include <stdio.h>
#include <memory.h>

struct factor{
    int p;
    int n; 
};

int prime[6000]; //PI(50000)<6000
bool flag[50000];// 50000^2 > 2^31 
factor f[500];

void getprime()
{
    int s = 0;
    memset(flag,false,sizeof(flag));
    for(int i=2;i<50000;i++)
    {
        if(!flag[i])
        {
            prime[s++] = i;
            for(unsigned int j=i*i;j<50000;j=j+i)
                flag[j] = true;
        }
    }
}
void getfactor(int m,int &g){
    g = 0;
    for(int i=0;prime[i]*prime[i]<=m;i++)
    {
        if(m%prime[i]==0)
        {
            f[g].p = prime[i];
            f[g].n++;
            m = m / prime[i];
            while(m%prime[i]==0)
            {
                f[g].n++;
                m = m / prime[i];
            }
            g++;
        }
        if(m == 1)
            break;
    }
    if(m>1)//m是大于50000的素数 
    {
        f[g].p=m;
        f[g].n++;
        g++;
    }
}
bool isdivided(int n,int m,int g){
    int pnum,t;
    for(int i=g-1;i>=0;i--){
        pnum = 0;
        t = f[i].p;
        while(n>=t){
            pnum = pnum + n / t;
            t = t * f[i].p;
        }
        if(pnum < f[i].n)
            return false;
    }
    return true;
}

int main()
{
    int n,m,i,g;
    getprime();
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(i=0;i<1000;i++){
            f[i].n=0;//因子初始化
        }
        if(n<=1 && m>1)
        {
            printf("%d does not divide %d!\n",m,n);
            continue;
        }
        if(m==0)
        {
            printf("%d does not divide %d!\n",m,n);
            continue;
        }
        if(n>=m)
        {
            printf("%d divides %d!\n",m,n);
            continue;
        }
        getfactor(m,g);
        if(isdivided(n,m,g))
            printf("%d divides %d!\n",m,n);
        else
            printf("%d does not divide %d!\n",m,n);
    }
    return 0;
}

ps：开始写了个t = t * t，导致一直报错Runtime Error SIGFPE。