1 #include <iostream>
 2 #include <cstdio>
 3 #include <cmath>
 4 #include <cstring>
 5 #include <algorithm>
 6 #include <queue>
 7 using namespace std;
 8 struct node
 9 {
10     int x, step;
11 }s,e;
12 int n, m,vis[10010];
13 int shushu(int k)
14 {
15     int t = sqrt(k);
 
16     for (int i = 2; i <= t; i++)
17     {
18         if (k%i == 0)
19             return 0;
20     }
21     return 1;
22 }
23 void bfs()
24 {
25     node temp, next;
26     queue<node>q;
27     q.push(s);
28     while (!q.empty())
29     {
30         temp = q.front(); q.pop();
31         if (temp.x == m)
 
32         {
33             printf("%d", temp.step);
34             return;
35         }
36         for (int i = 1; i < 10; i = i + 2)//枚舉個位
37         {
38             next.x = (temp.x / 10) * 10 + i;
39             if (next.x != temp.x&&vis[next.x] == 0 && shushu(next.x))
40             {
 
41                 vis[next.x] = 1;
42                 next.step = temp.step + 1;
43                 q.push(next);
44             }
45         }
46         for (int i = 0; i < 10; i++)//枚舉十位
47         {
48             next.x = (temp.x / 100) * 100 + i * 10 + temp.x % 10;
49             if (next.x != temp.x&&vis[next.x] == 0 && shushu(next.x))
50             {
51                 vis[next.x] = 1;
52                 next.step = temp.step + 1;
53                 q.push(next);
54             }
55         }
56         for (int i = 0; i < 10; i++)//枚舉百位
57         {
58             next.x = (temp.x / 1000) * 1000 + i * 100+ temp.x % 100;
59             if (next.x != temp.x&&vis[next.x] == 0 && shushu(next.x))
60             {
61                 vis[next.x] = 1;
62                 next.step = temp.step + 1;
63                 q.push(next);
64             }
65         }
66         for (int i = 1; i < 10; i++)//枚舉千位
67         {
68             next.x = i*1000 + temp.x % 1000;
69             if (next.x != temp.x&&vis[next.x] == 0 && shushu(next.x))
70             {
71                 vis[next.x] = 1;
72                 next.step = temp.step + 1;
73                 q.push(next);
74             }
75         }
76     }
77 }
78 int main()
79 {
80     int t;
81     scanf("%d",&t);
82     while (t--)
83     {
84         scanf("%d%d",&n,&m);
85         s.x = n;
86         memset(vis, 0, sizeof(vis));
87         vis[n] = 1;
88         s.step = 0;
89         bfs();
90         printf("\n");
91     }
92     return 0;
93 }

POJ 3126（BFS）