POJ3126Prime Path(BFS)

#include"cstdio"
#include"queue"
#include"cstring"
using namespace std;
const int MAXN=10000;
typedef pair<int,int> P;
int vis[MAXN];
int s,e;
bool prime(int x)
{
    for(int i=2;i*i<=x;i++)
    {
        if(x%i==0)
        {
            return false;
        }
    }
    return true;
}

void bfs()
{
    queue<P> que;
    que.push(P(0,s));
    vis[s]=1;
    while(!que.empty())
    {
        P now = que.front();que.pop();
        if(now.second==e)
        {
            printf("%d\n",now.first);
            return ;
        }

        int p=now.second%10;
        int pp=(now.second%100)/10;
        for(int i=1;i<=9;i+=2)    //枚举个位
        {
            int next=(now.second/10)*10+i;
            if(!vis[next]&&next!=now.second&&prime(next))
            {
                vis[next]=1;
                que.push(P(now.first+1,next));
            }
        }

        for(int i=0;i<=9;i++)    //枚举十位
        {
            int next=(now.second/100)*100+i*10+p;
            if(!vis[next]&&next!=now.second&&prime(next))
            {
                vis[next]=1;
                que.push(P(now.first+1,next));
            }

        }

        for(int i=0;i<=9;i++)    //枚举百位
        {
            int next=(now.second/1000)*1000+i*100+pp*10+p;
            if(!vis[next]&&next!=now.second&&prime(next))
            {
                vis[next]=1;
                que.push(P(now.first+1,next));
            }
        }

        for(int i=1;i<=9;i++)    //枚举千位
        {
            int next=i*1000+now.second%1000;
            if(!vis[next]&&next!=now.second&&prime(next))
            {
                vis[next]=1;
                que.push(P(now.first+1,next));
            }
        }
    }
    printf("Impossible\n");
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&s,&e);
        memset(vis,0,sizeof(vis));
        bfs();
    }
    return 0;
}