（Problem 41）Pandigital prime

We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once. For example, 2143 is a 4-digit pandigital and is also prime.

What is the largest n-digit pandigital prime that exists?

#include<stdio.h>
#include<math.h>
#include<string.h>
#include<ctype.h>
#include<stdlib.h>
#include<stdbool.h>

bool isprim(int n)
{
    int i=2;
    if(n==1) return false;
    for(; i*i<=n; i++)
    {
        if(n%i==0)  return false;
    }
    return true;
}

bool pandigital(int n)
{
    char s[10],d[10]={0};
    int i=0;
    sprintf(s,"%d",n);
    int len=strlen(s);
    while(i<len)
    {
        switch(s[i]-'0')
        {
            case 1: d[1]++;break;
            case 2: d[2]++;break;
            case 3: d[3]++;break;
            case 4: d[4]++;break;
            case 5: d[5]++;break;
            case 6: d[6]++;break;
            case 7: d[7]++;break;
            case 8: d[8]++;break;
            case 9: d[9]++;break;
            default: break;
        }
        i++;
    }
    for(i=1; i<=len; i++)
    {
        if(d[i]!=1)  return false;
    }
    if(!isprim(n))  return false;
    else return true;
}

int main()
{
    int i=10000001;
    while(i>1000)
    {
        if(pandigital(i))
        {
            printf("%d\n",i);
            break;
        }
        i=i-2;
    }
    return 0;
}

 

Answer:

7652413