poj 1129 Channel Allocation

 1 import java.util.*;
 2 import java.math.*;
 3 public class Main {
 4     public static boolean flag=false;
 5     public static int ans=0;
 6     public static void main(String []args)
 7     {
 8         Scanner cin=new Scanner(System.in);
 9         int n;
10         String str;
11         while(cin.hasNext())
12         {
13             ans=1;
14             int [][]g=new int[100][100];
15             int []hash=new int[100];
16              n=cin.nextInt();
17              if(n==0) break;
18              for(int i=0; i<n; i++)
19              {
20                  str=cin.next();
21                  for(int j=2; j<(int)str.length(); j++)
22                  {
23                      g[str.charAt(0)-‘A‘][str.charAt(j)-‘A‘]=1;
24                  }
25              }
26              flag=false;
27              dfs(0,1,g,n,hash);
28              if(ans==1)
29              {
30              System.out.println("1 channel needed.");
31              }
32              else
33              {
34                  System.out.println(ans+" channels needed.");
35              }
36         }
37     }
38     public static int deal(int id,int co,int n,int g[][],int hash[])
39     {
40         for(int i=0; i<n; i++)
41         {
42             if(g[id][i]==1&&co==hash[i])
43             {
44                 return 0;
45             }
46         }
47         return 1;
48     }
49     public static void dfs(int num,int m1,int g[][],int n,int hash[])
50     {
51         if(flag) return;
52         if(num>=n)
53         {
54             flag=true;
55             return;
56         }
57         for(int i=1; i<=m1; i++)
58         {
59             if(deal(num,i,n,g,hash)==1)
60             {
61                 hash[num]=i;
62                 dfs(num+1,m1,g,n,hash);
63                 hash[num]=0;
64             }
65         }
66         if(flag==false)
67         {
68             ans++;
69             dfs(num,m1+1,g,n,hash);
70         }
71     }
72 }