POJ-2570-Fiber Network

#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
const int maxn=201;
int n,a[maxn][maxn];
int main()
{
while(scanf("%d",&n)&&n)
{
memset(a,0,sizeof(a));
int ita,itb;
while(scanf("%d%d",&ita,&itb)&&(ita+itb))
{
char str[30];
scanf("%s",str);
for(int i=0;i<strlen(str);i++)
a[ita][itb]|=1<<(str[i]-'a');
}
for(int k=1;k<=n;k++)
for(int i=1;i<=n;i++)
for(int j=1;j<=n;j++)
a[i][j]|=a[i][k]&a[k][j];
while(scanf("%d%d",&ita,&itb)&&(ita+itb))
{
for(int i='a';i<='z';i++)
if(a[ita][itb]&(1<<(i-'a')))
printf("%c",i);
if(!a[ita][itb])
printf("-");
printf("\n");
}
printf("\n");
}
return 0;
}