POJ 1129 Channel Allocation 平面图染色问题

/*
ID: sdj22251
PROG: subset
LANG: C++
*/
#include <iostream>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <cmath>
#include <ctime>
#define MAXN 1005
#define INF 100000000
#define eps 1e-7
#define PI 3.1415926535898
using namespace std;
int color[27], n;
vector<int>v[27];
bool ok(int u)
{
int x = v[u].size();
for(int i = 0; i < x; i++)
{
if(color[v[u][i]] == color[u]) return false;
}
return true;
}
bool dfs(int u, int cnum)
{
if(u >= n || cnum == 4) return true;
else
{
for(int i = 1; i <= cnum; i++)
{
color[u] = i;
if(ok(u))
{
if(dfs(u + 1, cnum)) return true;
}
color[u] = 0;
}
}
return false;
}
int main()
{
char s[30];
while(scanf("%d", &n) != EOF && n)
{
memset(color, 0, sizeof(color));
for(int i = 0; i < n; i++)
v[i].clear();
for(int i = 0; i < n; i++)
{
scanf("%s", s);
int len = strlen(s);
for(int j = 2; j < len; j++)
{
v[i].push_back(s[j] - 'A');
}
}
for(int i = 1; i <= 4; i++)
{
if(dfs(0, i))
{
if(i == 1) printf("1 channel needed.\n");
else printf("%d channels needed.\n",i);
break;
}
}
}
return 0;
}