#include <bits/stdc++.h>
using namespace std;
 
int main() {
	int t;
	cin >> t;
	while(t--)
	{
		string s;
		int  k,n;
		cin >> n >> k;
		cin >> s;
		string st = s;
		reverse(st.begin(),st.end());
		map<char,int> m;
		for(int i=0;i<n;i++)
		{
			m[s[i]]++;
		}
		int sum=0;
		for(auto x : m)
		{
			sum = x.second;
		}
		if(n>1 && k>0 && sum!=n)
		{
			cout << "YES" << endl;
		}
		else if(s[0] < st[0])
		{
			cout << "YES" << endl;
		}
		else
		{
			cout << "NO" << endl;
		}
	}
	return 0;
}

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a
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string
6 0
theory
9 2
universal
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codeforcesecrofedoc
19 1
codeforcesecrofedoc
3 1
zzz