package test;

import java.io.*;

import java.util.*;

public class GeneString {

static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

public static int nextInt() throws IOException {

return Integer.parseInt(br.readLine());

}

public static int[] nextArr() throws IOException {

String elements[] = br.readLine().split(" ");

int arr[] = new int[elements.length];

for (int j = 0; j < elements.length; j++)

arr[j] = Integer.parseInt(elements[j]);

return arr;

}

public static void printArr(int arr[]) {

for (int i = 0; i < arr.length; i++)

System.out.print(arr);

}

public static String next() throws IOException {

return br.readLine();

}

public static Boolean validgene(ArrayList<Integer> gene, int n) {

for (int i = 0; i < gene.size(); i++) {

if (gene.get(i) > n) {

return false;

}

}

return true;

}

public static void main(String[] args) throws IOException {

int T = nextInt();

while (T-- > 0) {

int n = nextInt();

int ans = Integer.MAX_VALUE;

StringBuilder s = new StringBuilder(next());

StringBuilder extra = new StringBuilder();

HashMap<Character, Integer> hash = new HashMap<Character, Integer>();

for (int i = 0; i < s.length(); i++) {

if (!hash.containsKey(s.charAt(i)))

hash.put(s.charAt(i), 1);

else

hash.put(s.charAt(i), hash.get(s.charAt(i)) + 1);

if (hash.get(s.charAt(i)) > n / 4)

extra.append(s.charAt(i));

}

if (s.indexOf(extra.toString()) != -1)

System.out.println(extra.length());

else {

int left = 0, right = 0;

while (right < s.length()) {

System.out.println(hash);

hash.put(s.charAt(right), hash.get(s.charAt(right)) - 1);

right += 1;

while (validgene(new ArrayList<Integer>(hash.values()), (n / 4))) {

ans = Math.min(ans, right - left);

hash.put(s.charAt(left), hash.get(s.charAt(left)) + 1);

left += 1;

}

System.out.println(left + " " + right);

}

System.out.println(ans);

}

}

}

}