Problem: Polycarp has 26 tasks. Each task is designated by a capital letter of the Latin alphabet.

The teacher asked Polycarp to solve tasks in the following way: if Polycarp began to solve some task, then he must solve it to the end, without being distracted by another task. After switching to another task, Polycarp cannot return to the previous task.

Polycarp can only solve one task during the day. Every day he wrote down what task he solved. Now the teacher wants to know if Polycarp followed his advice.

For example, if Polycarp solved tasks in the following order: "DDBBCCCBBEZ", then the teacher will see that on the third day Polycarp began to solve the task 'B', then on the fifth day he got distracted and began to solve the task 'C', on the eighth day Polycarp returned to the task 'B'. Other examples of when the teacher is suspicious: "BAB", "AABBCCDDEEBZZ" and "AAAAZAAAAA".

If Polycarp solved the tasks as follows: "FFGZZZY", then the teacher cannot have any suspicions. Please note that Polycarp is not obligated to solve all tasks. Other examples of when the teacher doesn't have any suspicious: "BA", "AFFFCC" and "YYYYY".

Help Polycarp find out if his teacher might be suspicious.

Input

The first line contains an integer t (1 ≤ t ≤ 1000). Then t test cases follow.

The first line of each test case contains one integer n (1 ≤ n ≤ 50) — the number of days during which Polycarp solved tasks.

The second line contains a string of length n, consisting of uppercase Latin letters, which is the order in which Polycarp solved the tasks.

Output

For each test case output: 

  * "YES", if the teacher cannot be suspicious; 
  * "NO", otherwise. 



You may print every letter in any case you want (so, for example, the strings yEs, yes, Yes and YES are all recognized as positive answer).

Example

Input


5
3
ABA
11
DDBBCCCBBEZ
7
FFGZZZY
1
Z
2
AB


Output


NO
NO
YES
YES
YES

Solution (in JAVA):

Solution:
import java.io.*;
import java.util.*;

public class Stack2 {

    static class Reader {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader() {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1) {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }
            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException {
            if (din == null)
                return;
            din.close();
        }
    }

    static Reader sc = new Reader();
    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));

    public static void main(String[] args) throws IOException {
        /*
         * For integer input: int n=inputInt();
         * For long input: long n=inputLong();
         * For double input: double n=inputDouble();
         * For String input: String s=inputString();
         * Logic goes here
         * For printing without space: print(a+""); where a is a variable of any datatype
         * For printing with space: printSp(a+""); where a is a variable of any datatype
         * For printing with new line: println(a+""); where a is a variable of any datatype
         */
        Scanner sc = new Scanner(System.in);
        int t = sc.nextInt();
        for(int i=0;i<t;i++){
            int n=sc.nextInt();
            String s=sc.next();
            StringBuilder stringBuilder=new StringBuilder();
            char charprev=s.charAt(0);
            stringBuilder.append(charprev);
            for(int j=1;j<n;j++){
                char ch=s.charAt(j);
                if(ch!=charprev){
                    stringBuilder.append(ch);
                }
                charprev=ch;
            }
            String y=stringBuilder.toString();
            boolean[] check=new boolean[26];
            boolean flag=false;
            for(int j=0;j<y.length();j++){
                char ch=y.charAt(j);
                if(check[ch-'A']){
                    flag=true;
                    break;
                }
                check[ch-'A']=true;

            }
            if(flag){
                System.out.println("NO");
            }else {
                System.out.println("YES");
            }
        }

        bw.flush();
        bw.close();


    }

    public static void bfs(int r, int c, Queue<int[]> queue, long[][] dis, char[][] map, boolean[][] visited) {
        while (!queue.isEmpty()) {
            int[] ar = queue.poll();
            int x = ar[0];
            int y = ar[1];
            if (x + 1 < r) {
                if (map[x + 1][y] != 'T' && dis[x + 1][y] > (dis[x][y] + 1)) {
                    dis[x + 1][y] = Math.min(dis[x + 1][y], (dis[x][y] + 1));
                    queue.add(new int[]{x + 1, y});
                } /*else if (map[x][y] != map[x + 1][y] && dis[x + 1][y] > (dis[x][y] + 1)) {
                    dis[x + 1][y] = Math.min(dis[x + 1][y], dis[x][y] + 1);
                    queue.add(new int[]{x + 1, y});
                }*/
              /*  if(!visited[x+1][y] ){
                    queue.add(new int[]{x + 1, y});
                    visited[x+1][y]=true;
                }*/


            }
            if (y + 1 < c) {
                if (map[x][y + 1] != 'T' && dis[x][y + 1] > (dis[x][y] + 1)) {
                    dis[x][y + 1] = Math.min(dis[x][y + 1], dis[x][y] + 1);
                    queue.add(new int[]{x, y + 1});
                } /*else if (map[x][y] != map[x][y + 1] && dis[x][y + 1] > (dis[x][y] + 1)) {
                    dis[x][y + 1] = Math.min(dis[x][y + 1], dis[x][y] + 1);
                    queue.add(new int[]{x, y + 1});
                }*/
               /* if( !visited[x][y+1]){
                    queue.add(new int[]{x, y+1});
                    visited[x][y+1]=true;
                }*/


            }
            if (x - 1 >= 0) {
                if (map[x - 1][y] != 'T' && dis[x - 1][y] > (dis[x][y] + 1)) {
                    dis[x - 1][y] = Math.min(dis[x - 1][y], (dis[x][y] + 1));
                    queue.add(new int[]{x - 1, y});
                } /*else if (map[x][y] != map[x - 1][y] && dis[x - 1][y] > (dis[x][y] + 1)) {
                    dis[x - 1][y] = Math.min(dis[x - 1][y], dis[x][y] + 1);
                    queue.add(new int[]{x - 1, y});
                }*/
               /* if(!visited[x-1][y]){
                    queue.add(new int[]{x - 1, y});
                    visited[x-1][y]=true;
                }*/


            }
            if (y - 1 >= 0) {
                if (map[x][y - 1] != 'T' && dis[x][y - 1] > (dis[x][y] + 1)) {
                    dis[x][y - 1] = Math.min(dis[x][y - 1], (dis[x][y] + 1));
                    queue.add(new int[]{x, y - 1});
                } /*else if (map[x][y] != map[x][y - 1] && dis[x][y - 1] > (dis[x][y] + 1)) {
                    dis[x][y - 1] = Math.min(dis[x][y - 1], dis[x][y] + 1);
                    queue.add(new int[]{x, y - 1});
                }*/
               /* if(!visited[x][y-1]){
                    queue.add(new int[]{x , y-1});
                    visited[x][y-1]=true;
                }*/


            }
        }
    }


    public static void dfs1(List<List<Integer>> g, boolean[] visited, Stack<Integer> stack, int num) {
        visited[num] = true;
        for (Integer integer : g.get(num)) {
            if (!visited[integer]) {
                dfs1(g, visited, stack, integer);
            }
        }
        stack.push(num);
    }

    public static void dfs2(List<List<Integer>> g, boolean[] visited, List<Integer> list, int num, int c, int[] raj) {
        visited[num] = true;

        for (Integer integer : g.get(num)) {
            if (!visited[integer]) {
                dfs2(g, visited, list, integer, c, raj);
            }
        }
        raj[num] = c;
        list.add(num);

    }

    public static int inputInt() throws IOException {
        return sc.nextInt();
    }

    public static long inputLong() throws IOException {
        return sc.nextLong();
    }

    public static double inputDouble() throws IOException {
        return sc.nextDouble();
    }

    public static String inputString() throws IOException {
        return sc.readLine();
    }

    public static void print(String a) throws IOException {
        bw.write(a);
    }

    public static void printSp(String a) throws IOException {
        bw.write(a + " ");
    }

    public static void println(String a) throws IOException {
        bw.write(a + "\n");
    }


    public static long getAns(int[] ar, int c, long[][] dp, int i, int sign) {
        if (i < 0) {
            return 1;
        }

        if (c <= 0) {
            return 1;
        }

        dp[i][c] = Math.max(dp[i][c], Math.max(ar[i] * getAns(ar, c - 1, dp, i - 1, sign), getAns(ar, c, dp, i - 1, 1)));
        return dp[i][c];
    }


    public static long power(long a, long b, long c) {
        long ans = 1;
        while (b != 0) {
            if (b % 2 == 1) {
                ans = ans * a;
                ans %= c;
            }
            a = a * a;
            a %= c;
            b /= 2;
        }
        return ans;
    }

    public static long power1(long a, long b, long c) {
        long ans = 1;
        while (b != 0) {
            if (b % 2 == 1) {
                ans = multiply(ans, a, c);
            }
            a = multiply(a, a, c);
            b /= 2;

        }
        return ans;

    }

    public static long multiply(long a, long b, long c) {
        long res = 0;
        a %= c;
        while (b > 0) {
            if (b % 2 == 1) {
                res = (res + a) % c;
            }
            a = (a + a) % c;
            b /= 2;
        }

        return res % c;

    }

    public static long totient(long n) {
        long result = n;
        for (long i = 2; i * i <= n; i++) {
            if (n % i == 0) {
                //sum=sum+2*i;
                while (n % i == 0) {
                    n /= i;
                    // sum=sum+n;
                }
                result -= result / i;

            }
        }
        if (n > 1) {
            result -= result / n;

        }
        return result;
    }


    public static long gcd(long a, long b) {
        if (b == 0) {
            return a;
        } else {
            return gcd(b, a % b);
        }
    }

    public static boolean[] primes(int n) {
        boolean[] p = new boolean[n + 1];
        p[0] = false;
        p[1] = false;
        for (int i = 2; i <= n; i++) {
            p[i] = true;
        }

        for (int i = 2; i * i <= n; i++) {
            if (p[i]) {
                for (int j = i * i; j <= n; j += i) {
                    p[j] = false;
                }
            }

        }
        return p;
    }

}