poj 1129(dfs+图的四色定理)

1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 
 7 bool map[33][33];
 8 int mark[33];
 9 char str[33];
10 int n,ans;
11 
12 bool Judge(int x,int color)
13 {
14     for(int i=0;i<n;i++){
15         if(i!=x&&map[x][i]&&mark[i]==color)
16             return 0;
17     }
18     return 1;
19 }
20 
21 void dfs(int pos)
22 {
23     if(pos==n){
24         ans=min(ans,*max_element(mark,mark+n));
25         return ;
26     }
27     for(int i=pos;i<n;i++){
28         for(int j=1;j<=4;j++){
29             if(Judge(i,j)){
30                 mark[i]=j;
31                 dfs(i+1);
32             }
33         }
34     }
35 }
36 
37 
38 int main()
39 {
40     while(~scanf("%d",&n)&&n){
41         memset(map,false,sizeof(map));
42         for(int i=0;i<n;i++){
43             scanf("%s",str);
44             for(int j=2;j<strlen(str);j++){
45                 map[i][str[j]-'A']=true;
46                 map[str[j]-'A'][i]=true;
47             }
48         }
49         memset(mark,0,sizeof(mark));
50         ans=4;
51         mark[0]=1;
52         dfs(1);
53         if(ans==1){
54             printf("1 channel needed.\n");
55         }else 
56             printf("%d channels needed.\n",ans);
57     }
58     return 0;
59 }      

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