poj 1129 Channel Allocation

http://poj.org/problem?id=1129

 import java.util.*;
 import java.math.*;
 public class Main {
     public static boolean flag=false;
     public static int ans=0;
     public static void main(String []args)
     {
         Scanner cin=new Scanner(System.in);
         int n;
         String str;
         while(cin.hasNext())
         {
             ans=1;
             int [][]g=new int[100][100];
             int []hash=new int[100];
              n=cin.nextInt();
              if(n==0) break;
              for(int i=0; i<n; i++)
              {
                  str=cin.next();
                  for(int j=2; j<(int)str.length(); j++)
                  {
                      g[str.charAt(0)-'A'][str.charAt(j)-'A']=1;
                  }
              }
              flag=false;
              dfs(0,1,g,n,hash);
              if(ans==1)
              {
              System.out.println("1 channel needed.");
              }
              else
              {
                  System.out.println(ans+" channels needed.");
              }
         }
     }
     public static int deal(int id,int co,int n,int g[][],int hash[])
     {
         for(int i=0; i<n; i++)
         {
             if(g[id][i]==1&&co==hash[i])
             {
                 return 0;
             }
         }
         return 1;
     }
     public static void dfs(int num,int m1,int g[][],int n,int hash[])
     {
         if(flag) return;
         if(num>=n)
         {
             flag=true;
             return;
         }
         for(int i=1; i<=m1; i++)
         {
             if(deal(num,i,n,g,hash)==1)
             {
                 hash[num]=i;
                 dfs(num+1,m1,g,n,hash);
                 hash[num]=0;
             }
         }
         if(flag==false)
         {
             ans++;
             dfs(num,m1+1,g,n,hash);
         }
     }
 }