Poj3126--bfs

POJ 1326-digit bfsprime Path

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 12480		Accepted: 7069

Description

The ministers of the Cabinet were quite upset by the message from the chief of Security stating, they would all has T o 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 had 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

31033 81791373 80171033 1033

Sample Output

670

Test instructions: The shortest number of steps required from a four-digit prime number to another four-digit prime number, each step can only change one digit, and the number of changes must be four-digit number
This is a typical digital search problem, to find the shortest circuit so with BFS, the difficulty lies in the conversion of analog number, and also pay attention to the border control

#include <iostream>#include<cstdlib>#include<cstdio>#include<cstring>#include<algorithm>#include<queue>using namespacestd;Const intmaxn=10000;intn,m;BOOLVIS[MAXN];intans;structnode{intNum,step;};intMypow (intNintk) {    intres=1;  while(k--) res*=N; returnRes;}BOOLIsPrime (intN//Judging prime numbers, because the data is not big, too lazy to print the prime list{     for(intI=2; i*i<=n;i++){        if(n%i==0)return false; }    return true;}intChangeintNintIintJ//the conversion of analog number, there are many techniques, must be careful{    intF=n/mypow (Ten, i+1) *mypow (Ten, i+1);//Reserved Prefixes    intR=n%mypow (Ten, i);//reserved suffix    intMid=j*mypow (Ten, i);//Change the middle number    returnF+mid+R;}BOOLBFs () {memset (Vis,0,sizeof(VIS)); Queue<node>Q; Q.push ({n,0}); Vis[n]=1;  while(!Q.empty ()) {Node now=Q.front ();        Q.pop (); if(now.num==m) {ans=Now.step; return true; }         for(intI=0;i<4; i++) {//from 1th Place to fourth place             for(intj=0; j<=9; j + +) {//change the position number to J                intnextnum=Change (NOW.NUM,I,J); if(nextnum< +|| NEXTNUM&GT;=MAXN)Continue;//border Control                if(vis[nextnum]| |! IsPrime (Nextnum))Continue; Vis[nextnum]=1; Q.push ({nextnum,now.step+1}); }        }    }    return false;}intMain () {intT;cin>>T;  while(t--) {cin>>n>>m; if(BFS ()) cout<<ans<<Endl; Elsecout<<"Impossible"<<Endl; }    return 0;}

Poj3126_bfs

Poj3126--bfs