POJ 3126 Prime Path 素数筛，bfs

题目： http://poj.org/problem?id=3126

困得不行了，没想到敲完一遍直接就A了，16ms，debug环节都没进行。人品啊。

 #include <stdio.h>
 #include <string.h>
 #include <queue>
 using namespace std;
 
 bool prime[];
 int vis[];
 int s, t;
 
 void prime_init()
 {
     memset(prime, , sizeof(prime));
     prime[] = ;
     for(int i = ; i < ; i += )
         prime[i] = ;
     for(int i = ; i < ; i += )
     {
         if(prime[i])
         {
             for(int j = i*i; j < ; j += i+i)
                 prime[j] = ;
         }
     }
 }
 
 queue<int>q;
 void bfs()
 {
     while(!q.empty())q.pop();
     memset(vis, , sizeof(vis));
     q.push(s);
     vis[s] = ;
     while(!q.empty())
     {
         int u = q.front();
         q.pop();
         if(u == t)
         {
             printf("%d\n", vis[u]-);
             return;
         }
         int a = u % ;
         int b = u %  - a;
         int c = u %  - a - b;
         int d = u - u % ;
         for(int i = u-a; i <= u-a+; i++)
         {
             if(prime[i] && !vis[i])
             {
                 q.push(i);
                 vis[i] = vis[u] + ;
             }
         }
         for(int i = u-b; i <= u-b+; i += )
         {
             if(prime[i] && !vis[i])
             {
                 q.push(i);
                 vis[i] = vis[u] + ;
             }
         }
         for(int i = u-c; i <= u-c+; i += )
         {
             if(prime[i] && !vis[i])
             {
                 q.push(i);
                 vis[i] = vis[u] + ;
             }
         }
         for(int i = u-d+; i <= u-b+; i += )
         {
             if(prime[i] && !vis[i])
             {
                 q.push(i);
                 vis[i] = vis[u] + ;
             }
         }
     }
 }
 
 int main()
 {
     prime_init();
     int n;
     scanf("%d", &n);
     while(n--)
     {
         scanf("%d %d", &s, &t);
         bfs();
     }
     return ;
 }