3-Blast Palindrome

#include <bits/stdc++.h>

using namespace std;

#define ll     long long
#define _test   int _TEST; cin>>_TEST; while(_TEST--)

int main()
{
    _test
    {
        int n;
        string s;
        cin>>n>>s;

        if(n%3 == 1)
        {
            cout<<"YES\n";
            continue;
        }

        if(n%3 == 2)
        {
            multiset<char> mst;
            for(int i=1; i<n; i+=3)
                mst.insert(s[i]);

            int f = 0;

            for(int i=0; i<n && f==0; i+=3)
            {
                if(mst.find(s[i]) != mst.end())
                    f = 1;

                mst.erase(mst.find(s[i+1]));
            }

            if(f)
                cout<<"YES\n";
            else
                cout<<"NO\n";

            continue;
        }


        multiset<char> mst;
        for(int i=2; i<n; i+=3)
            mst.insert(s[i]);

        int f = 0;

        for(int i=0; i<n && f==0; i+=3)
        {
            if(mst.find(s[i]) != mst.end())
                f = 1;

            mst.erase(mst.find(s[i+2]));
        }

        if(f)
            cout<<"YES\n";
        else
            cout<<"NO\n";
    }
}