（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?

 1 #include<stdio.h>

 2 #include<math.h>

 3 #include<string.h>

 4 #include<ctype.h>

 5 #include<stdlib.h>

 6 #include<stdbool.h>

 7 

 8 bool isprim(int n)

 9 {

10     int i=2;

11     if(n==1) return false;

12     for(; i*i<=n; i++)

13     {

14         if(n%i==0)  return false;

15     }

16     return true;

17 }

18 

19 bool pandigital(int n)

20 {

21     char s[10],d[10]={0};

22     int i=0;

23     sprintf(s,"%d",n);

24     int len=strlen(s);

25     while(i<len)

26     {

27         switch(s[i]-'0')

28         {

29             case 1: d[1]++;break;

30             case 2: d[2]++;break;

31             case 3: d[3]++;break;

32             case 4: d[4]++;break;

33             case 5: d[5]++;break;

34             case 6: d[6]++;break;

35             case 7: d[7]++;break;

36             case 8: d[8]++;break;

37             case 9: d[9]++;break;

38             default: break;

39         }

40         i++;

41     }

42     for(i=1; i<=len; i++)

43     {

44         if(d[i]!=1)  return false;

45     }

46     if(!isprim(n))  return false;

47     else return true;

48 }

49 

50 int main()

51 {

52     int i=10000001;

53     while(i>1000)

54     {

55         if(pandigital(i))

56         {

57             printf("%d\n",i);

58             break;

59         }

60         i=i-2;

61     }

62     return 0;

63 }

 

Answer:

7652413