POJ3126Prime Path(BFS)

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

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

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

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

        }

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

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