t=int(input())
result=[]
for i1 in range(t):
n=int(input())
task_list=input()
current_task=task_list[0]
tasks_done=[current_task]
pointer=1
while pointer<n:
if current_task!=task_list[pointer]:
if task_list[pointer] in tasks_done:
result.append("NO")
break
else:
tasks_done.append(current_task)
current_task=task_list[pointer]
pointer+=1
else:
result.append("YES")
for i2 in result:
print(i2)
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb push_back
int main()
{
ll t,n;string s;cin>>t;
while(t--){
cin>>n>>s;
vector<ll> v;set<ll> l;
for(ll i = 0;i<n;i++){
v.pb(s[i]);l.insert(s[i]);
while(i+1<n&&s[i]==s[i+1]){
i++;
}
}
if(l.size()==v.size()){
cout<<"YES";
}
else{
cout<<"NO";
}
cout<<'\n';
}
}368B - Sereja and Suffixes | 1665C - Tree Infection |
1665D - GCD Guess | 29A - Spit Problem |
1097B - Petr and a Combination Lock | 92A - Chips |
1665B - Array Cloning Technique | 1665A - GCD vs LCM |
118D - Caesar's Legions | 1598A - Computer Game |
1605A - AM Deviation | 1461A - String Generation |
1585B - Array Eversion | 1661C - Water the Trees |
1459A - Red-Blue Shuffle | 1661B - Getting Zero |
1661A - Array Balancing | 1649B - Game of Ball Passing |
572A - Arrays | 1455A - Strange Functions |
1566B - MIN-MEX Cut | 678C - Joty and Chocolate |
1352E - Special Elements | 1520E - Arranging The Sheep |
1157E - Minimum Array | 1661D - Progressions Covering |
262A - Roma and Lucky Numbers | 1634B - Fortune Telling |
1358A - Park Lighting | 253C - Text Editor |