#include<bits/stdc++.h>
using namespace std ;
int main(){
    int t ;
    cin>>t;
    while(t--){
        bool isDone = false ;
        int n ;
        cin>>n ;
        string s ;
        cin>>s;
        map <string,int> mp;
        for(int i = 0 ; i< n-1 ; i++){ 
            string temp = s.substr(i,2);
            if(mp[temp] == 0)mp[temp] = i+1;
            // checking if there is already a pair exist or not if yes then
            // difference between their indexes should be greater than or equal to 2 else test as :- aaa will fail 
            else if(mp[temp] + 2 <= i+1){
                cout<<"YES\n";
                isDone = true ;
                break;
            }
        }
        if(!isDone) cout<<"NO\n";       
    }
}

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6
10
codeforces
8
labacaba
5
uohhh
16
isthissuffixtree
1
x
4
momo