1.Link:

2.Content:

Prime Path

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 11757		Accepted: 6675

Description

The ministers of the cabinet were quite upset by the message from the Chief of Security stating that they would all have to change the four-digit room numbers on their offices. 

— It is a matter of security to change such things every now and then, to keep the enemy in the dark. 

— But look, I have chosen my number 1033 for good reasons. I am the Prime minister, you know! 

— I know, so therefore your new number 8179 is also a prime. You will just have to paste four new digits over the four old ones on your office door. 

— No, it’s not that simple. Suppose that I change the first digit to an 8, then the number will read 8033 which is not a prime! 

— I see, being the prime minister you cannot stand having a non-prime number on your door even for a few seconds. 

— Correct! So I must invent a scheme for going from 1033 to 8179 by a path of prime numbers where only one digit is changed from one prime to the next prime.

Now, the minister of finance, who had been eavesdropping, intervened. 

— No unnecessary expenditure, please! I happen to know that the price of a digit is one pound. 

— Hmm, in that case I need a computer program to minimize the cost. You don't know some very cheap software gurus, do you? 

— In fact, I do. You see, there is this programming contest going on... Help the prime minister to find the cheapest prime path between any two given four-digit primes! The first digit must be nonzero, of course. Here is a solution in the case above. 

1033

1733

3733

3739

3779

8779

8179

The cost of this solution is 6 pounds. Note that the digit 1 which got pasted over in step 2 can not be reused in the last step – a new 1 must be purchased.

Input

One line with a positive number: the number of test cases (at most 100). Then for each test case, one line with two numbers separated by a blank. Both numbers are four-digit primes (without leading zeros).

Output

One line for each case, either with a number stating the minimal cost or containing the word Impossible.

Sample Input

31033 81791373 80171033 1033

Sample Output

670

Source

3.Method:

4.Code:

1 #include
     
       2 #include
      
        3 using namespace std; 4 #define MAX 10002 5 //#define MAX 102 6 int a[MAX]; 7 int b[MAX]; 8 int main() 9 {10     int n,m;11     int i,j;12     int x,y;13     int k;14     queue
       
         q;15     a[2]=0; 16     for(i=4;i
        
         >n;34     for(int ii=0;ii
         
          >x>>y;37         for(j=0;j
          
           =1000)54 {55 //printf("perfect");56 b[m+j*k]=b[m]+1;57 q.push(m+j*k);58 }59 }60 }61 }62 q.pop();63 }64 cout<
           
            <
           
          
         
        
       
      
     

 

5.Reference: