poj1129Channel Allocation

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

四色定理  最多有四色 从1到四搜

#include <iostream>
#include<cstdio>
#include<cstring>
#include<stdlib.h>
using namespace std;
int n,w[100][100],co[100],mi,flag;
void dfs(int x,int v)
{
    int i,j,f,k=v;
    if(flag)
    return ;
    if(x>n)
    {
        mi = v;
        flag = 1;
        return ;
    }
    else
    {
        for(i = 1; i <= 4 ; i++)
        {
            f = 1;
            for(j = 1; j <= n ; j++)
                if(w[x][j]&&co[j]==i)
                {
                    f =0 ;
                    break;
                }
            if(f)
            {
                co[x] = i;
                if(k>i)
                   dfs(x+1,k);
                else
                   dfs(x+1,i);
                co[x] = 0;
            }
        }
    }
}
int main()
{
    int i,j,k,c,m;
    char s[50];
    while(cin>>n)
    {
        memset(w,0,sizeof(w));
        flag = 0;
        if(!n) break;
        m = n;
        while(m--)
        {
            cin>>s;
            k = strlen(s);
            c = s[0]+1-'A';
            for(i = 2 ; i < k ; i++)
            {
                j = s[i]+1-'A';
                w[c][j] = 1;
                w[j][c] = 1;
            }
        }
        dfs(1,1);
        if(mi==1)
        printf("1 channel needed.\n");
        else
        printf("%d channels needed.\n",mi);
    }
    return 0;
}