description: Grandma Capa has decided to knit a scarf and asked Grandpa Sher to make a pattern for it, a pattern is a string consisting of lowercase English letters. Grandpa Sher wrote a string s of length n.
  
  Grandma Capa wants to knit a beautiful scarf, and in her opinion, a beautiful scarf can only be knit from a string that is a palindrome. She wants to change the pattern written by Grandpa Sher, but to avoid offending him, she will choose one lowercase English letter and erase some (at her choice, possibly none or all) occurrences of that letter in string s.
  
  She also wants to minimize the number of erased symbols from the pattern. Please help her and find the minimum number of symbols she can erase to make string s a palindrome, or tell her that it's impossible. Notice that she can only erase symbols equal to the one letter she chose.
  
  A string is a palindrome if it is the same from the left to the right and from the right to the left. For example, the strings 'kek', 'abacaba', 'r' and 'papicipap' are palindromes, while the strings 'abb' and 'iq' are not.
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 100) — the number of test cases. The next 2 ⋅ t lines contain the description of test cases. The description of each test case consists of two lines.
  
  The first line of each test case contains a single integer n (1 ≤ n ≤ 10^5) — the length of the string.
  
  The second line of each test case contains the string s consisting of n lowercase English letters.
  
  It is guaranteed that the sum of n over all test cases does not exceed 2 ⋅ 10^5.
  
  Output
  
  For each test case print the minimum number of erased symbols required to make the string a palindrome, if it is possible, and -1, if it is impossible.
  
  Example
  
  Input
  
  
  5
  8
  abcaacab
  6
  xyzxyz
  4
  abba
  8
  rprarlap
  10
  khyyhhyhky
  
  
  Output
  
  
  2
  -1
  0
  3
  2
  
  Note
  
  In the first test case, you can choose a letter 'a' and erase its first and last occurrences, you will get a string 'bcaacb', which is a palindrome. You can also choose a letter 'b' and erase all its occurrences, you will get a string 'acaaca', which is a palindrome as well.
  
  In the second test case, it can be shown that it is impossible to choose a letter and erase some of its occurrences to get a palindrome.
  
  In the third test case, you don't have to erase any symbols because the string is already a palindrome.
solution: import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;
  import java.io.IOException;import java.io.InputStream;import java.io.PrintWriter;
  import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;
  import java.lang.reflect.Array;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;import java.security.AccessControlException;import java.util.Arrays;
  import java.util.Collection;import java.util.Comparator;import java.util.List;import java.util.Map;
  import java.util.Objects;import java.util.TreeMap;import java.util.function.Function;
  import java.util.stream.Collectors;import java.util.stream.IntStream;import java.util.stream.LongStream;
  import java.util.stream.Stream;public class _C {static public void main(final String[] args) 
  throws IOException{C._main(args);}
  static class C extends Solver{public C(){}@Override public void solve()throws IOException
  {int n=sc.nextInt();sc.nextLine();int[]s=sc.nextLine().chars().toArray();int res
  =-1;TreeMap<Integer,List<Integer>>mapi=Datas.mapi(s);List<Integer>list=mapi.keySet().stream().collect(Collectors.toList());
  list.add(0,(int)'#');l:for(int k:list){int start=0;int end=s.length-1;int count=
  0;while(start<end){if(s[start]!=s[end]){if(s[start]==k){start++;count++;continue
  ;}if(s[end]==k){end--;count++;continue;}continue l;}start++;end--;}if(k=='#'){res
  =0;break;}if(res==-1 || count<res){res=count;}}pw.println(res);}static public void 
  _main(String[]args)throws IOException{new C().run();}}static class Datas{final static 
  String SPACE=" ";public static TreeMap<Integer,Integer>mapc(final int[]a){return 
  IntStream.range(0,a.length).collect(()->new TreeMap<Integer,Integer>(),(res,i)->
  {res.put(a[i],res.getOrDefault(a[i],0)+1);},Map::putAll);}public static TreeMap<Long,
  Integer>mapc(final long[]a){return IntStream.range(0,a.length).collect(()->new TreeMap<Long,
  Integer>(),(res,i)->{res.put(a[i],res.getOrDefault(a[i],0)+1);},Map::putAll);}public 
  static<T>TreeMap<T,Integer>mapc(final T[]a,Comparator<T>cmp){return IntStream.range(0,
  a.length).collect(cmp!=null?()->new TreeMap<T,Integer>(cmp):()->new TreeMap<T,Integer>(),
  (res,i)->{res.put(a[i],res.getOrDefault(a[i],0)+1);},Map::putAll);}public static
  <T>TreeMap<T,Integer>mapc(final T[]a){return mapc(a,null);}public static TreeMap<Integer,
  Integer>mapc(final IntStream a){return a.collect(()->new TreeMap<Integer,Integer>(),
  (res,v)->{res.put(v,res.getOrDefault(v,0)+1);},Map::putAll);}public static TreeMap<Long,
  Integer>mapc(final LongStream a){return a.collect(()->new TreeMap<Long,Integer>(),
  (res,v)->{res.put(v,res.getOrDefault(v,0)+1);},Map::putAll);}public static<T>TreeMap<T,
  Integer>mapc(final Stream<T>a,Comparator<T>cmp){return a.collect(cmp!=null?()->new 
  TreeMap<T,Integer>(cmp):()->new TreeMap<T,Integer>(),(res,v)->{res.put(v,res.getOrDefault(v,
  0)+1);},Map::putAll);}public static<T>TreeMap<T,Integer>mapc(final Stream<T>a){return 
  mapc(a,null);}public static<T>TreeMap<T,Integer>mapc(final Collection<T>a,Comparator<T>
  cmp){return mapc(a.stream(),cmp);}public static<T>TreeMap<T,Integer>mapc(final Collection<T>
  a){return mapc(a.stream());}public static TreeMap<Integer,List<Integer>>mapi(final 
  int[]a){return IntStream.range(0,a.length).collect(()->new TreeMap<Integer,List<Integer>>(),
  (res,i)->{if(!res.containsKey(a[i])){res.put(a[i],Stream.of(i).collect(Collectors.toList()));
  }else{res.get(a[i]).add(i);}},Map::putAll);}public static TreeMap<Long,List<Integer>>
  mapi(final long[]a){return IntStream.range(0,a.length).collect(()->new TreeMap<Long,
  List<Integer>>(),(res,i)->{if(!res.containsKey(a[i])){res.put(a[i],Stream.of(i).collect(Collectors.toList()));
  }else{res.get(a[i]).add(i);}},Map::putAll);}public static<T>TreeMap<T,List<Integer>>
  mapi(final T[]a,Comparator<T>cmp){return IntStream.range(0,a.length).collect(cmp
  !=null?()->new TreeMap<T,List<Integer>>(cmp):()->new TreeMap<T,List<Integer>>(),
  (res,i)->{if(!res.containsKey(a[i])){res.put(a[i],Stream.of(i).collect(Collectors.toList()));
  }else{res.get(a[i]).add(i);}},Map::putAll);}public static<T>TreeMap<T,List<Integer>>
  mapi(final T[]a){return mapi(a,null);}public static TreeMap<Integer,List<Integer>>
  mapi(final IntStream a){int[]i=new int[]{0};return a.collect(()->new TreeMap<Integer,
  List<Integer>>(),(res,v)->{if(!res.containsKey(v)){res.put(v,Stream.of(i[0]).collect(Collectors.toList()));
  }else{res.get(v).add(i[0]);}i[0]++;},Map::putAll);}public static TreeMap<Long,List<Integer>>
  mapi(final LongStream a){int[]i=new int[]{0};return a.collect(()->new TreeMap<Long,
  List<Integer>>(),(res,v)->{if(!res.containsKey(v)){res.put(v,Stream.of(i[0]).collect(Collectors.toList()));
  }else{res.get(v).add(i[0]);}i[0]++;},Map::putAll);}public static<T>TreeMap<T,List<Integer>>
  mapi(final Stream<T>a,Comparator<T>cmp){int[]i=new int[]{0};return a.collect(cmp
  !=null?()->new TreeMap<T,List<Integer>>(cmp):()->new TreeMap<T,List<Integer>>(),
  (res,v)->{if(!res.containsKey(v)){res.put(v,Stream.of(i[0]).collect(Collectors.toList()));
  }else{res.get(v).add(i[0]);}i[0]++;},Map::putAll);}public static<T>TreeMap<T,List<Integer>>
  mapi(final Stream<T>a){return mapi(a,null);}public static<T>TreeMap<T,List<Integer>>
  mapi(final Collection<T>a,Comparator<T>cmp){return mapi(a.stream(),cmp);}public 
  static<T>TreeMap<T,List<Integer>>mapi(final Collection<T>a){return mapi(a.stream());
  }public static List<int[]>listi(final int[]a){return IntStream.range(0,a.length).mapToObj(i
  ->new int[]{a[i],i}).collect(Collectors.toList());}public static List<long[]>listi(final 
  long[]a){return IntStream.range(0,a.length).mapToObj(i->new long[]{a[i],i}).collect(Collectors.toList());
  }public static<T>List<Pair<T,Integer>>listi(final T[]a){return IntStream.range(0,
  a.length).mapToObj(i->new Pair<T,Integer>(a[i],i)).collect(Collectors.toList());
  }public static List<int[]>listi(final IntStream a){int[]i=new int[]{0};return a.mapToObj(v
  ->new int[]{v,i[0]++}).collect(Collectors.toList());}public static List<long[]>listi(final 
  LongStream a){int[]i=new int[]{0};return a.mapToObj(v->new long[]{v,i[0]++}).collect(Collectors.toList());
  }public static<T>List<Pair<T,Integer>>listi(final Stream<T>a){int[]i=new int[]{0};
  return a.map(v->new Pair<T,Integer>(v,i[0]++)).collect(Collectors.toList());}public 
  static<T>List<Pair<T,Integer>>listi(final Collection<T>a){int[]i=new int[]{0};return 
  a.stream().map(v->new Pair<T,Integer>(v,i[0]++)).collect(Collectors.toList());}public 
  static String join(final int[]a){return Arrays.stream(a).mapToObj(Integer::toString).collect(Collectors.joining(SPACE));
  }public static String join(final long[]a){return Arrays.stream(a).mapToObj(Long::toString).collect(Collectors.joining(SPACE));
  }public static<T>String join(final T[]a){return Arrays.stream(a).map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
  }public static<T>String join(final T[]a,final Function<T,String>toString){return 
  Arrays.stream(a).map(v->toString.apply(v)).collect(Collectors.joining(SPACE));}public 
  static<T>String join(final Collection<T>a){return a.stream().map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
  }public static<T>String join(final Collection<T>a,final Function<T,String>toString)
  {return a.stream().map(v->toString.apply(v)).collect(Collectors.joining(SPACE));
  }public static<T>String join(final Stream<T>a){return a.map(v->Objects.toString(v)).collect(Collectors.joining(SPACE));
  }public static<T>String join(final Stream<T>a,final Function<T,String>toString){
  return a.map(v->toString.apply(v)).collect(Collectors.joining(SPACE));}public static
  <T>String join(final IntStream a){return a.mapToObj(Integer::toString).collect(Collectors.joining(SPACE));
  }public static<T>String join(final LongStream a){return a.mapToObj(Long::toString).collect(Collectors.joining(SPACE));
  }public static List<Integer>list(final int[]a){return Arrays.stream(a).mapToObj(Integer::valueOf).collect(Collectors.toList());
  }public static List<Integer>list(final IntStream a){return a.mapToObj(Integer::valueOf).collect(Collectors.toList());
  }public static List<Long>list(final long[]a){return Arrays.stream(a).mapToObj(Long::valueOf).collect(Collectors.toList());
  }public static List<Long>list(final LongStream a){return a.mapToObj(Long::valueOf).collect(Collectors.toList());
  }public static<T>List<T>list(final Stream<T>a){return a.collect(Collectors.toList());
  }public static<T>List<T>list(final Collection<T>a){return a.stream().collect(Collectors.toList());
  }public static<T>List<T>list(final T[]a){return Arrays.stream(a).collect(Collectors.toList());
  }public static String yesNo(final boolean res){return res?"YES":"NO";}public static 
  String dump(Object obj){String res="";if(obj!=null){Class cl=obj.getClass();String 
  cls=cl.getName();if(cls.startsWith("[")){res+="[";for(int i=0;;i++){try{Object o
  =Array.get(obj,i);String s=dump(o);if(i>0){res+=", ";}res+=s;}catch(ArrayIndexOutOfBoundsException 
  ex){break;}}res+="]";}else if(Collection.class.isAssignableFrom(cl)){@SuppressWarnings("unchecked")final 
  Object s=((Collection)obj).stream().map(v->dump(v)).collect(Collectors.joining(", ",
  "[","]"));res+=s.toString();}else if(Map.class.isAssignableFrom(cl)){@SuppressWarnings("unchecked")final 
  Object s=((Map)obj).entrySet().stream().map(v->dump(v)).collect(Collectors.joining(", ",
  "{","}"));res+=s.toString();}else if(Character.class.isInstance(obj)|| Integer.class.isInstance(obj)
  || Long.class.isInstance(obj)|| Float.class.isInstance(obj)|| Double.class.isInstance(obj)|| String.class.isInstance(obj)
  ){res+=Objects.toString(obj);}else if(Map.Entry.class.isInstance(obj)){res+=dump(((Map.Entry)obj).getKey())
  +"="+dump(((Map.Entry)obj).getValue());}else if(Stream.class.isInstance(obj)){@SuppressWarnings("unchecked")
  final Object s=((Stream)obj).map(v->dump(v)).collect(Collectors.joining(", ","[",
  "]"));res+=s.toString();}else{res+=Stream.concat(Arrays.stream(obj.getClass().getFields()).map(v
  ->{String name=v.getName();String val;try{Object o=v.get(obj);if(o!=null && v.isAnnotationPresent(Dump.class))
  {Dump an=v.getAnnotation(Dump.class);Class ocl=o.getClass();val="{";for(String fn:an.fields())
  {try{Field f=ocl.getField(fn);val+=fn+"="+dump(f.get(o))+", ";}catch(NoSuchFieldException 
  nsfex){try{@SuppressWarnings("unchecked")final Method m=ocl.getMethod(fn);val+=fn+"="+dump(m.invoke(o))
  +", ";}catch(NoSuchMethodException | IllegalArgumentException | InvocationTargetException 
  nsmex){}}}if(val.endsWith(", ")){val=val.substring(0,val.length()-2);}val+="}";}
  else{val=dump(o);}}catch(IllegalAccessException ex){val="N/A";}return name+"="+val;
  }),Arrays.stream(obj.getClass().getMethods()).filter(m->m.isAnnotationPresent(Getter.class)).map(m
  ->{String name=m.getName();String val;try{Object o=m.invoke(obj);if(o!=null && m.isAnnotationPresent(Dump.class))
  {Dump an=m.getAnnotation(Dump.class);Class ocl=o.getClass();val="{";for(String fn:an.fields())
  {try{Field f=ocl.getField(fn);val+=fn+"="+dump(f.get(o))+", ";}catch(NoSuchFieldException 
  nsfex){try{@SuppressWarnings("unchecked")final Method m1=ocl.getMethod(fn);val+=fn+"="+dump(m1.invoke(o))
  +", ";}catch(NoSuchMethodException | IllegalArgumentException | InvocationTargetException 
  nsmex){}}}if(val.endsWith(", ")){val=val.substring(0,val.length()-2);}val+="}";}else
  {val=dump(o);}}catch(IllegalAccessException | InvocationTargetException ex){val=
  "N/A";}return name+"="+val;})).collect(Collectors.joining(", ","{"+obj.getClass().getName()
  +": ","}"));}}if(res.length()==0){res="<null>";}return res;}}@Retention(RetentionPolicy.RUNTIME)
  public @interface Dump{String[]fields();}@Retention(RetentionPolicy.RUNTIME)public @interface Getter{}static class 
  Pair<K,V>{private K k;private V v;public Pair(final K t,final V u){this.k=t;this.v
  =u;}public K getKey(){return k;}public V getValue(){return v;}public void setKey(K 
  t){k=t;}public void setValue(V t){v=t;}}static class MyScanner{private StringBuilder 
  cache=new StringBuilder();int cache_pos=0;private int first_linebreak=-1;private 
  int second_linebreak=-1;private StringBuilder sb=new StringBuilder();private InputStream 
  is=null;public MyScanner(final InputStream is){this.is=is;}public String charToString(final 
  int c){return String.format("'%s'",c=='\n'?"\\n":(c=='\r'?"\\r":String.valueOf((char)c)));
  }public int get(){int res=-1;if(cache_pos<cache.length()){res=cache.charAt(cache_pos);
  cache_pos++;if(cache_pos==cache.length()){cache.delete(0,cache_pos);cache_pos=0;
  }}else{try{res=is.read();}catch(IOException ex){throw new RuntimeException(ex);}
  }return res;}private void unget(final int c){if(cache_pos==0){cache.insert(0,(char)c);
  }else{cache_pos--;}}public String nextLine(){sb.delete(0,sb.length());int c;boolean 
  done=false;boolean end=false;while((c=get())!=-1){if(check_linebreak(c)){done=true;
  if(c==first_linebreak){if(!end){end=true;}else{cache.append((char)c);break;}}else 
  if(second_linebreak!=-1 && c==second_linebreak){break;}}if(end && c!=first_linebreak 
  && c!=second_linebreak){cache.append((char)c);break;}if(!done){sb.append((char)c);
  }}return!done && sb.length()==0?null:sb.toString();}private boolean check_linebreak(int 
  c){if(c=='\n'|| c=='\r'){if(first_linebreak==-1){first_linebreak=c;}else if(c!=first_linebreak 
  && second_linebreak==-1){second_linebreak=c;}return true;}return false;}public int 
  nextInt(){return Integer.parseInt(next());}public long nextLong(){return Long.parseLong(next());
  }public boolean hasNext(){boolean res=false;int c;while((c=get())!=-1){if(!check_linebreak(c)
  && c!=' '&& c!='\t'){res=true;unget(c);break;}}return res;}public String next(){
  sb.delete(0,sb.length());boolean started=false;int c;while((c=get())!=-1){if(check_linebreak(c)
  || c==' '|| c=='\t'){if(started){unget(c);break;}}else{started=true;sb.append((char)c);
  }}return sb.toString();}public int nextChar(){return get();}public boolean eof()
  {int c=get();boolean res=false;if(c!=-1){unget(c);}else{res=true;}return res;}public 
  double nextDouble(){return Double.parseDouble(next());}}static abstract class Solver
  {protected String nameIn=null;protected String nameOut=null;protected boolean singleTest
  =false;protected MyScanner sc=null;protected PrintWriter pw=null;private int current_test
  =0;private int count_tests=0;protected int currentTest(){return current_test;}protected 
  int countTests(){return count_tests;}private void process()throws IOException{if(!singleTest)
  {count_tests=sc.nextInt();sc.nextLine();for(current_test=1;current_test<=count_tests;
  current_test++){solve();pw.flush();}}else{count_tests=1;current_test=1;solve();}
  }abstract protected void solve()throws IOException;public void run()throws IOException
  {boolean done=false;try{if(nameIn!=null){if(new File(nameIn).exists()){try(FileInputStream 
  fis=new FileInputStream(nameIn);PrintWriter pw0=select_output();){select_output();
  done=true;sc=new MyScanner(fis);pw=pw0;process();}}else{throw new RuntimeException("File "
  +new File(nameIn).getAbsolutePath()+" does not exist!");}}}catch(IOException | AccessControlException 
  ex){}if(!done){try(PrintWriter pw0=select_output();){sc=new MyScanner(System.in);
  pw=pw0;process();}}}private PrintWriter select_output()throws FileNotFoundException
  {if(nameOut!=null){return new PrintWriter(nameOut);}return new PrintWriter(System.out);
  }}static abstract class Tester{static public int getRandomInt(final int min,final 
  int max){return(min+(int)Math.floor(Math.random()*(max-min+1)));}static public long 
  getRandomLong(final long min,final long max){return(min+(long)Math.floor(Math.random()
  *(max-min+1)));}static public double getRandomDouble(final double min,final double 
  maxExclusive){return(min+Math.random()*(maxExclusive-min));}abstract protected void 
  testOutput(final List<String>output_data);abstract protected void generateInput();
  abstract protected String inputDataToString();private boolean break_tester=false;
  protected void beforeTesting(){}protected void breakTester(){break_tester=true;}
  public boolean broken(){return break_tester;}}}
  