poj 1129 Channel Allocation
http://poj.org/problem?id=1129
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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 }