uva :124 - Following Orders

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;

void dfs(bool path[][26],int indegre[],bool used[],char ans[],int numofcharacter,int position)
{
    if(numofcharacter==position)
    {
       //printf("%d\n",position);
        for(int i=0;i<numofcharacter;i++)
        printf("%c",ans[i]+'a');
        printf("\n");
        return;
    }
    for(int i=0;i<26;i++)
    {
        if(used[i]&&!indegre[i])
        {
            used[i]=false;
            for(int j=0;j<26;j++)
            {
                if(used[j]&&path[i][j])
                {
                    indegre[j]--;
                }
            }
            ans[position]=i;
            dfs(path,indegre,used,ans,numofcharacter,position+1);
            used[i]=true;
            for(int j=0;j<26;j++)
            if(used[j]&&path[i][j])
            indegre[j]++;
        }
    }
}

int main()
{
   // freopen("input.txt","r",stdin);
    char a[10000];
    int y=0;
    while(gets(a)!=NULL)
    {
        if(y>1)printf("\n");
        y=10;
        bool path[26][26];
        bool used[26];
        char ans[26],*p1,*p2;
        int indegre[26],c=0;
        for(int i=0;i<26;i++)
        {
            used[i]=false;
            indegre[i]=0;
            for(int j=0;j<26;j++)
            {
                path[i][j]=0;
            }
        }
        p1=strtok(a," \n");
        while(p1)
        {
            char ch=p1[0];
            used[ch-'a']=true;
            p1=strtok(NULL," \n");
            c++;
        }
        gets(a);
        p1=strtok(a," \n");
        while(p1)
        {
            char ch,ph;
            ch=p1[0];
            p1=strtok(NULL," \n");
            ph=p1[0];
            p1=strtok(NULL," \n");
            path[ch-'a'][ph-'a']=true;
            indegre[ph-'a']++;
        }
        dfs(path,indegre,used,ans,c,0);
    }
    return 0;
}