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## baneHunter

Posted by 1340502116 at 2016-07-18 15:05:09 on Problem 3126
```#include <iostream>
#include <queue>
#include <string.h>
using namespace std;
const int MAXN=10005;
struct Node{
int x,step;
Node(){}
Node(int x,int step)
{
this->x=x;
this->step=step;
}
};
int src,ter;
int vis[MAXN];
bool isPrime(int x)
{
if(x<1000)	return false;
for(int i=2;i*i<=x;i++)
{
if(x%i==0)	return false;
}
return true;
}
void bfs()
{
memset(vis,0,sizeof(vis));
queue<Node> que;
que.push(Node(src,0));
vis[src]=1;
while(!que.empty())
{
Node now=que.front();que.pop();
if(now.x==ter)
{
cout<<now.step<<endl;
return ;
}
int buf[2][4];
buf[0][0]=(now.x/1000)*1000;
buf[0][1]=((now.x/100)%10)*100;
buf[0][2]=((now.x%100)/10)*10;
buf[0][3]=now.x%10;
buf[1][0]=1000;
buf[1][1]=100;
buf[1][2]=10;
buf[1][3]=1;
for(int i=0;i<4;i++)
{
int tmp=0;
for(int j=0;j<4;j++)
{
if(i==j)	continue;
tmp+=buf[0][j];
}
for(int j=0;j<=9;j++)
{
int net=tmp+buf[1][i]*j;
if(!vis[net]&&isPrime(net))
{
vis[net]=1;
que.push(Node(net,now.step+1));
}
}
}
}
cout<<"Impossible"<<endl;
}
int main()
{
int T;
cin>>T;
while(T--)
{
cin>>src>>ter;
bfs();
}
return 0;
}```

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