Prime Path (BFS)

  1 #include <iostream>
  2 #include <string>
  3 #include <cstring>
  4 #include <queue>
  5 #include <stdio.h>
  6 
  7 using namespace std;
  8 
  9 const int N = 10010;
 10 typedef struct Node{
 11     int val;
 12     int cnt;
 13 }Node;
 14 
 15 int T;
 16 int a[N],prime[N],vis[N];
 17 int tot,p;
 18 int n = 10000;
 19 int m;
 20 
 21 bool one_digit(int l,int r) // 判断是否只有一位数不同
 22 {
 23     int sum = 0;
 24     int temp1,temp2;
 25     while (l!=0)
 26     {
 27         temp1 = l%10;
 28         temp2 = r%10;
 29         if (temp1!=temp2)
 30             sum++;
 31         l /= 10;
 32         r /= 10;
 33     }
 34     if (sum==1)
 35         return true;
 36     return false;
 37 }
 38 
 39 
 40 
 41 int bfs()
 42 {
 43     queue<Node> q;
 44     Node node;
 45     //   memset(vis,0, sizeof(vis));
 46     node.val = n;
 47     node.cnt = 0;
 48     q.push(node);
 49     vis[node.val] = 1;
 50     while (!q.empty())
 51     {
 52         Node cur = q.front();
 53         q.pop();
 54         if (cur.val == m)
 55             return cur.cnt;
 56         for (int i=p-1;i>=0;i--)
 57         {
 58             Node next = cur;
 59             if (!vis[prime[i]] && one_digit(next.val,prime[i]))
 60             {
 61                 vis[prime[i]] = 1;
 62                 next.val = prime[i];
 63                 next.cnt++;
 64                 q.push(next);
 65             }
 66         }
 67     }
 68     return -1;
 69 }
 70 
 71 
 72 int main()
 73 {
 74     // 埃筛
 75     for (int i=2;i<=n;i++)
 76     {
 77         if (!vis[i])
 78         {
 79             a[tot++] = i;
 80             for (int j=2*i;j<=n;j+=i)
 81                 vis[j] = 1;
 82         }
 83     }
 84     for (int i=0;i<tot;i++)
 85     {
 86         if (a[i]>1000)
 87             prime[p++] = a[i];
 88     }
 89     cin >> T;
 90     while (T--)
 91     {
 92         cin >> n >> m;
 93         memset(vis,0, sizeof(vis));
 94         int ant = bfs();
 95         if (ant<0)
 96         {
 97             printf("Impossible\n");
 98         }
 99         else
100             printf("%d\n",ant);
101     }
102 }