BFS POJ 3126 Prime Path

题目传送门

 /*
     题意：从一个数到另外一个数，每次改变一个数字，且每次是素数
     BFS：先预处理1000到9999的素数，简单BFS一下。我没输出Impossible都AC，数据有点弱
 */
 /************************************************
 Author        :Running_Time
 Created Time  :2015-8-2 15:46:57
 File Name     :POJ_3126.cpp
 *************************************************/

 #include <cstdio>
 #include <algorithm>
 #include <iostream>
 #include <sstream>
 #include <cstring>
 #include <cmath>
 #include <string>
 #include <vector>
 #include <queue>
 #include <deque>
 #include <stack>
 #include <list>
 #include <map>
 #include <set>
 #include <bitset>
 #include <cstdlib>
 #include <ctime>
 using namespace std;

 #define lson l, mid, rt << 1
 #define rson mid + 1, r, rt << 1 | 1
 typedef long long ll;
 const int MAXN = 1e4 + ;
 const int INF = 0x3f3f3f3f;
 const int MOD = 1e9 + ;
 bool is_prime[MAXN];
 bool vis[MAXN];
 int x, y, res;
 struct Digit    {
     int d[];
     int step;
 };

 void solve(void)    {
     memset (is_prime, true, sizeof (is_prime));
     for (int i=; i<=; ++i)  {
         for (int j=; j<i; ++j)  {
             if (i % j == ) {
                 is_prime[i] = false;    break;
             }
         }
     }
 }

 int get_num(int *a) {
     int ret = ;
     for (int i=; i<=; ++i)    {
         ret = ret *  + a[i];
     }
     return ret;
 }

 void BFS(int u, int v)   {
     Digit tmp;
     for (int i=; i>=; --i)    {
         tmp.d[i] = u % ;  u /= ;
     }
     tmp.step = ;
     queue<Digit> Q; Q.push (tmp);   vis[u] = true;
     int ans = -;
     while (!Q.empty ()) {
         Digit x = Q.front ();   Q.pop ();
         int m = get_num (x.d);
         if (m == v) {
             ans = x.step;   break;
         }
         for (int i=; i<=; ++i)    {
             for (int j=; j<=; ++j)    {
                 if (i ==  && j == )   continue;
                 if (x.d[i] != j)    {
                     Digit y = x;
                     y.d[i] = j; m = get_num (y.d);
                     if (is_prime[m] && !vis[m])    {
                         vis[m] = true;  y.step++;   Q.push (y);
                     }
                 }
             }
         }
     }
     if (ans == -)  puts ("Impossible");
     else    printf ("%d\n", ans);
 }

 int main(void)    {       //POJ 3126 Prime Path
     solve ();
     int T;  scanf ("%d", &T);
     while (T--) {
         scanf ("%d%d", &x, &y);
         memset (vis, false, sizeof (vis));
         BFS (x, y);
     }

     return ;
 }