UVA - Phone List (vector)

#include<bits/stdc++.h>
using namespace std;
#define fastread() (ios_base::sync_with_stdio(false),cin.tie(NULL));
int main()
{
    fastread()
    int t;
    cin>>t;
    for(int j=1;j<=t;j++)
    {
        vector<string>phn;
        int n;
        cin>>n;
        string s;
        for(int i=0;i<n;i++)
        {
            cin>>s;
            phn.push_back(s);
        }
        sort(phn.begin(),phn.end());
        bool x=false;
        for(int i=0;i<n-1;i++)
        {
            s= phn[i+1].substr(0,phn[i].size());
            if(s==phn[i])
            {
                x=true;
                break;
            }
        }
        printf("Case %d: ",j);
        if(x)printf("NO\n");
        else printf("YES\n");
    }
}