POJ3126 Prime Path playing table +bfs

Description

The ministers of the Cabinet were quite upset by the message from the chief of Security stating, they would all hav E To change the four-digit-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 has 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'll just has to paste four new digits over the four old ones on your office door.
-no, it's not so simple. Suppose that I change the first digit to an 8 and then the number would read 8033 which is not a prime!
-I see, being the Prime Minister you cannot stand have 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 the prime numbers where only one digit are 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 then the price of a digit is one pound.
-HMM, in this case I need a computer program to minimize the cost. You don ' t know some very cheap software gurus?
-in fact, I do. You see, there are this programming contest going on ... Help the Prime minister to find the cheapest prime path between any and given Four-digit primes! The first digit must be nonzero, of course. Here's 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 step 2 can is reused in the last Step–a new 1 must is purchased.

Input

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

Output

Either with a number stating the minimal cost or containing the word impossible.

Sample Input

3
1033 8179
1373 8017
1033 1033

Sample Output

6
7
0

Title Description

To two four-digit number A, each change a one in a and after the change must be a prime number, ask the minimum number of changes can be to B? (never reach B on output impossible)

Thinking of solving problems

First, hit a prime list, and then use the queue to simulate the search process, the depth of the search into the structure, you can better output the number of changes.

Code

#include <cstdio>#include <cstring>#include <queue>using namespace STD;Const intMAXN =10010;BOOLPRIME[MAXN];BOOLVIS[MAXN];BOOLIsfind;intCntstructnum {intCint  Floor;}; queue<num>Que;num A, B;voidBFsvoid){//1033 8179    //que:2033 3033 ... 0033 1133 1233...1933 1043 1053 ... 1023 1034 ... 1032Que.push (a); while(!que.empty ()) {//p = 1033num p = que.front (); Que.pop ();if(P.c <= +|| !PRIME[P.C] | | VIS[P.C])Continue; VIS[P.C] =true;if(p.c = = B.C) {Isfind =true; CNT = P. Floor;return; } for(inti =1; I <Ten;            i + +) {num tmp; TMP.C = (p.c+ +*i)%10000; Tmp. Floor= P. Floor+1;            Que.push (TMP); TMP.C = (p.c/ +)* ++ (p.c% ++ -*i)% +;            Que.push (TMP); TMP.C = (p.c/ -)* -+ (p.c% -+Ten*i)% -;            Que.push (TMP); TMP.C = (p.c/Ten)*Ten+ (p.c%Ten+i)%Ten;        Que.push (TMP); }    }}intMain () {prime[0] = prime[1] =false; for(inti =2; i < MAXN; i + +) prime[i] =true; for(inti =2; I*i <= MAXN; i + +) {if(!prime[i])Continue; for(intj = i*2; J < Maxn; J + = i) {Prime[j] =false; }    }intTscanf("%d", &t); while(t--) {//InitializeCNT =0; Isfind =false; while(!que.empty ()) Que.pop ();memset(Vis,false,sizeof(VIS));scanf("%d%d", &AMP;A.C,&AMP;B.C);if(A.C = = B.C) {printf("0\n");Continue; } BFS ();if(Isfind)printf("%d\n", CNT);Else printf("impossible\n"); }return 0;}

POJ3126 Prime Path playing table +bfs