pku 1129 Channel Allocation(回溯（经典的图着色问题）)

#include <iostream>
using namespace std;
bool map[26][26];
int n,ans;
int color[26];
bool check(int position,int color_index)
{
for(int i=0;i<n;i++)
{
if(map[position][i]&&color[i]==color_index) return false;
}
return true;
}
void DFS(int index,int used_color_num)
{
if(used_color_num>=ans) return;
if(index==n)
{
ans=used_color_num;
return;
}
for(int i=1;i<=used_color_num;i++)
{
if(check(index,i))
{
color[index]=i;
DFS(index+1,used_color_num);
color[index]=0;
}
}
used_color_num++;
color[index]=used_color_num;
DFS(index+1,used_color_num);
color[index]=0;
}
int main()
{
char temp_str[30];
while(scanf("%d",&n)&&n)
{
memset(map,0,sizeof(map));
memset(color,0,sizeof(color));
ans=INT_MAX;
for(int i=0;i<n;i++)
{
scanf("%s",temp_str);
for(int j=2;temp_str[j]!='/0';j++)
{
map[i][temp_str[j]-'A']=true;
}
}
DFS(0,0);
if(ans==1) printf("%d channel needed./n",ans);
else printf("%d channels needed./n",ans);
}
return 0;
}