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。

 1 #include <stdio.h>
 2 #include <string.h>
 3 #include <queue>
 4 using namespace std;
 5 
 6 bool prime[10000];
 7 int vis[10000];
 8 int s, t;
 9 
10 void prime_init()
11 {
12     memset(prime, 1, sizeof(prime));
13     prime[1] = 0;
14     for(int i = 4; i < 10000; i += 2)
15         prime[i] = 0;
16     for(int i = 3; i < 100; i += 2)
17     {
18         if(prime[i])
19         {
20             for(int j = i*i; j < 10000; j += i+i)
21                 prime[j] = 0;
22         }
23     }
24 }
25 
26 queue<int>q;
27 void bfs()
28 {
29     while(!q.empty())q.pop();
30     memset(vis, 0, sizeof(vis));
31     q.push(s);
32     vis[s] = 1;
33     while(!q.empty())
34     {
35         int u = q.front();
36         q.pop();
37         if(u == t)
38         {
39             printf("%d\n", vis[u]-1);
40             return;
41         }
42         int a = u % 10;
43         int b = u % 100 - a;
44         int c = u % 1000 - a - b;
45         int d = u - u % 1000;
46         for(int i = u-a; i <= u-a+9; i++)
47         {
48             if(prime[i] && !vis[i])
49             {
50                 q.push(i);
51                 vis[i] = vis[u] + 1;
52             }
53         }
54         for(int i = u-b; i <= u-b+90; i += 10)
55         {
56             if(prime[i] && !vis[i])
57             {
58                 q.push(i);
59                 vis[i] = vis[u] + 1;
60             }
61         }
62         for(int i = u-c; i <= u-c+900; i += 100)
63         {
64             if(prime[i] && !vis[i])
65             {
66                 q.push(i);
67                 vis[i] = vis[u] + 1;
68             }
69         }
70         for(int i = u-d+1000; i <= u-b+9000; i += 1000)
71         {
72             if(prime[i] && !vis[i])
73             {
74                 q.push(i);
75                 vis[i] = vis[u] + 1;
76             }
77         }
78     }
79 }
80 
81 int main()
82 {
83     prime_init();
84     int n;
85     scanf("%d", &n);
86     while(n--)
87     {
88         scanf("%d %d", &s, &t);
89         bfs();
90     }
91     return 0;
92 }
View Code

 

posted @ 2013-08-19 15:06  Anti-Magic  阅读(177)  评论(0)  编辑  收藏  举报