description: As their story unravels, a timeless tale is told once again...
  
  Shirahime, a friend of Mocha's, is keen on playing the music game Arcaea and sharing Mocha interesting puzzles to solve. This day, Shirahime comes up with a new simple puzzle and wants Mocha to solve them. However, these puzzles are too easy for Mocha to solve, so she wants you to solve them and tell her the answers. The puzzles are described as follow.
  
  There are n squares arranged in a row, and each of them can be painted either red or blue.
  
  Among these squares, some of them have been painted already, and the others are blank. You can decide which color to paint on each blank square.
  
  Some pairs of adjacent squares may have the same color, which is imperfect. We define the imperfectness as the number of pairs of adjacent squares that share the same color.
  
  For example, the imperfectness of "BRRRBBR" is 3, with "BB" occurred once and "RR" occurred twice.
  
  Your goal is to minimize the imperfectness and print out the colors of the squares after painting. 
  
  Input
  
  Each test contains multiple test cases. 
  
  The first line contains a single integer t (1 ≤ t ≤ 100) — the number of test cases. Each test case consists of two lines.
  
  The first line of each test case contains an integer n (1≤ n≤ 100) — the length of the squares row.
  
  The second line of each test case contains a string s with length n, containing characters 'B', 'R' and '?'. Here 'B' stands for a blue square, 'R' for a red square, and '?' for a blank square.
  
  Output
  
  For each test case, print a line with a string only containing 'B' and 'R', the colors of the squares after painting, which imperfectness is minimized. If there are multiple solutions, print any of them.
  
  Example
  
  Input
  
  
  5
  7
  ?R???BR
  7
  ???R???
  1
  ?
  1
  B
  10
  ?R??RB??B?
  
  
  Output
  
  
  BRRBRBR
  BRBRBRB
  B
  B
  BRRBRBBRBR
  
  Note
  
  In the first test case, if the squares are painted "BRRBRBR", the imperfectness is 1 (since squares 2 and 3 have the same color), which is the minimum possible imperfectness.
solution: //Some of the methods are copied from GeeksforGeeks Website  
  import java.util.*;
  import java.lang.*;
  import java.io.*;
  public class Main
  { 
    //static Scanner sc=new Scanner(System.in)
    //static  Reader sc=new Reader();
    static FastReader sc=new FastReader(System.in);
    
    static long mod = (long)(1e9)+ 7;
    static int max_num=(int)1e5+5;
    static int solve(char a[],int n)
     {
        int ans=0;
        char pre=a[0];
        int seg=0;
        for(int i=1;i<n;i++)
          {
             char cur=a[i];
             if(pre==cur)
              seg++;
            else
             {
                ans+=seg;
                seg=0;
             }
            pre=cur;
          }
        ans+=seg;
        //out.println(new String(a));
        return ans;
     }
   public static void main (String[] args) throws java.lang.Exception
     {
  	try{
  	    /*
  	        int n=sc.nextInt();
  	        Collections.sort(al,Collections.reverseOrder());
  	     
  	        long n=sc.nextLong();
  	        String s=sc.next();
  	        StringBuilder sb=new StringBuilder();
  	     */
  		  int t = sc.nextInt();
  		  while(t-->0)
  		    { 
  		       int n=sc.nextInt();
  		       String s=sc.next();
  		       if(n==1)
  		         {
  		            if(s.equals("?"))
  		             out.println("R");
  		            else
  		             out.println(s);
  		          continue;
  		         }
  		       char ori[]=s.toCharArray();
  		       boolean all=true;
  		       for(int i=0;i<n;i++)
  		         {
  		            if(ori[i]!='?')
  		              {
  		                 all=false;
  		                 break;
  		              }
  		         }
  		       String sss=s;
  		       if(all)
  		        {
  		           ori[0]='R';
  		           sss=new String(ori);
  		        }
  		       char a[]=sss.toCharArray();
  		       char a2[]=sss.toCharArray();
  		       
  		       
  		       
  		       char pre=a[0];
  		       for(int i=1;i<n;i++)
  		         {
  		           char cur=a[i];
  		           if(cur=='?')
  		            {
  		               if(pre=='R')
  		                 a[i]='B';
  		                else
  		                 a[i]='R';
  		            }
  		           pre=a[i];
  		         }
  		    //  if(a[0]=='?')
  		    //   {
  		    //      if(a[1]=='R')
  		    //       a[0]='B';
  		    //      else
  		    //       a[0]='R';
  		    //   }
  		    char last=a[n-1];
  		    for(int i=n-2;i>=0;i--)
  		      {
  		         if(a[i]=='?')
  		          {
  		              if(last=='R')
  		                 a[i]='B';
  		              else
  		                 a[i]='R';
  		          }
  		       last=a[i];
  		      }
  		      String ss=new String(a);
  		      
  		      
  		       char pre2=a2[0];
  		       for(int i=1;i<n;i++)
  		         {
  		           char cur=a2[i];
  		           if(cur=='?')
  		            {
  		               if(pre2=='B')
  		                 a2[i]='R';
  		                else
  		                 a2[i]='B';
  		            }
  		           pre2=a2[i];
  		         }
  		    //  if(a2[0]=='?')
  		    //   {
  		    //      if(a2[1]=='B')
  		    //       a2[0]='R';
  		    //      else
  		    //       a2[0]='B';
  		    //   }
  		     char last2=a2[n-1];
  		    for(int i=n-2;i>=0;i--)
  		      {
  		         if(a2[i]=='?')
  		          {
  		              if(last2=='B')
  		                 a2[i]='R';
  		              else
  		                 a2[i]='B';
  		          }
  		       last2=a2[i];
  		      }
  		      String ss2=new String(a2);
  		      
  		      
  		      int ans1=solve(a,n);
  		      int ans2=solve(a2,n);
  		      
  		      //out.println(ans1+" "+ans2);
  		      if(ans1<=ans2)
  		      out.println(ss);
  		      else
  		      out.println(ss2);
  		    }
  	     out.flush();
  	     out.close();
  	   }     
  	catch(Exception e)
  		 {}
  	}
   
   /*
     ...SOLUTION ENDS HERE...........SOLUTION ENDS HERE...
   */
   
  static void flag(boolean flag)
     {
         out.println(flag ? "YES" : "NO");
         out.flush();
     }
     
   /*                     
      Map<Long,Long> map=new HashMap<>();
               for(int i=0;i<n;i++)
                 {
                    if(!map.containsKey(a[i]))
                     map.put(a[i],1);
                   else
                     map.replace(a[i],map.get(a[i])+1);
                 }
       
      Set<Map.Entry<Long,Long>> hmap=map.entrySet();
               for(Map.Entry<Long,Long> data : hmap)
                 {
            
                 }
         
     */
     
  //  static class Pair
  //    {
  //       int x,y;
  //       Pair(int x,int y)
  //        {
  //           this.x=x;
  //           this.y=y;
  //        }
  //    }
  
  //  Arrays.sort(p, new Comparator<Pair>()
  //     {
  //        @Override
  //        public int compare(Pair o1,Pair o2)
  //        {
  //           if(o1.x>o2.x) return 1;
  //           else if(o1.x==o2.x)
  //             {
  //                if(o1.y>o2.y) return 1;
  //                else return -1;
  //              }
  //           else return -1;
  //       }});
  
  static void print(int a[])
    {
       int n=a.length;
       for(int i=0;i<n;i++)
         {
            out.print(a[i]+" ");
         }
       out.println();
       out.flush();
    }
  static void print(long a[])
    {
       int n=a.length;
       for(int i=0;i<n;i++)
         {
            out.print(a[i]+" ");
         }
       out.println();
       out.flush();
    } 
  static void print_int(ArrayList<Integer> al)
    {
       int si=al.size();
       for(int i=0;i<si;i++)
         {
            out.print(al.get(i)+" ");
         }
       out.println();
       out.flush();
    }
  static void print_long(ArrayList<Long> al)
    {
       int si=al.size();
       for(int i=0;i<si;i++)
         {
            out.print(al.get(i)+" ");
         }
       out.println();
       out.flush();
    }
    
  static int LowerBound(int a[], int x) 
   { // x is the target value or key
    int l=-1,r=a.length;
    while(l+1<r) {
      int m=(l+r)>>>1;
      if(a[m]>=x) r=m;
      else l=m;
    }
    return r;
  }
  
   static int UpperBound(int a[], int x)
    {// x is the key or target value
      int l=-1,r=a.length;
      while(l+1<r) {
         int m=(l+r)>>>1;
         if(a[m]<=x) l=m;
         else r=m;
      }
      return l+1;
   }
  static void DFS(ArrayList<Integer> graph[],boolean[] visited, int u)
  	{
          visited[u]=true;
          int v=0;
          for(int i=0;i<graph[u].size();i++)
          {
              v=graph[u].get(i);
              if(!visited[v])
                 DFS(graph,visited,v);
          }
    } 
  static boolean[] prime(int num)
   {
  	      boolean[] bool = new boolean[num];
  		     
  		      for (int i = 0; i< bool.length; i++) {
  		         bool[i] = true;
  		      }
  		      for (int i = 2; i< Math.sqrt(num); i++) {
  		         if(bool[i] == true) {
  		            for(int j = (i*i); j<num; j = j+i) {
  		               bool[j] = false;
  		            }
  		         }
  		      }
  		      if(num >= 0) {
  		    	  bool[0] = false;
  		    	  bool[1] = false;
  		      }
  		      
  		      return bool;
    }
  static long nCr(long a,long b,long mod)
  {
   return (((fact[(int)a] * modInverse(fact[(int)b],mod))%mod * modInverse(fact[(int)(a - b)],mod))%mod + mod)%mod;
  }
  static long fact[]=new long[max_num];
  static void fact_fill()
   {
     long fact[]=new long[max_num];
     fact[0]=1l;
  	for(int i=1;i<max_num;i++)
  	  {
  	    fact[i]=(fact[i-1]*(long)i);
  	    if(fact[i]>=mod)
  	      fact[i]%=mod;
  	  } 
   }
  static long modInverse(long a, long m)
  	    {
  	       return power(a, m - 2, m);
  	    }
  static long power(long x, long y, long m)
  	    {
  	        if (y == 0)
  	            return 1;
  	        long p = power(x, y / 2, m) % m;
  	        p = (long)((p * (long)p) % m);
  	        if (y % 2 == 0)
  	            return p;
  	        else
  	            return (long)((x * (long)p) % m);
  	    }
  static long sum_array(int a[])
   {
      int n=a.length;
      long sum=0;
      for(int i=0;i<n;i++)
       sum+=a[i];
      return sum;
   }
  static long sum_array(long a[])
   {
      int n=a.length;
      long sum=0;
      for(int i=0;i<n;i++)
       sum+=a[i];
      return sum;
   }
  
  static void sort(int[] a) 
     {
  		ArrayList<Integer> l=new ArrayList<>();
  		for (int i:a) l.add(i);
  		Collections.sort(l);
  		for (int i=0; i<a.length; i++) a[i]=l.get(i);
  	}
  static void sort(long[] a) 
     {
  		ArrayList<Long> l=new ArrayList<>();
  		for (long i:a) l.add(i);
  		Collections.sort(l);
  		for (int i=0; i<a.length; i++) a[i]=l.get(i);
  	}
  
  static void reverse_array(int a[])
   {
      int n=a.length;
      int i,t; 
      for (i = 0; i < n / 2; i++) { 
              t = a[i]; 
              a[i] = a[n - i - 1]; 
              a[n - i - 1] = t; 
          } 
   }
  static void reverse_array(long a[])
   {
      int n=a.length;
      int i; long t; 
      for (i = 0; i < n / 2; i++) { 
              t = a[i]; 
              a[i] = a[n - i - 1]; 
              a[n - i - 1] = t; 
          } 
   }
  
  static long gcd(long a, long b) 
      { 
          if (a == 0) 
              return b; 
            
          return gcd(b%a, a); 
      } 
  static int gcd(int a, int b) 
      { 
          if (a == 0) 
              return b; 
            
          return gcd(b%a, a); 
      } 
  
     static class FastReader{
   
          byte[] buf = new byte[2048];
          int index, total;
          InputStream in;
   
          FastReader(InputStream is) {
              in = is;
          }
   
          int scan() throws IOException {
              if (index >= total) {
                  index = 0;
                  total = in.read(buf);
                  if (total <= 0) {
                      return -1;
                  }
              }
              return buf[index++];
          }
   
          String next() throws IOException {
              int c;
              for (c = scan(); c <= 32; c = scan());
              StringBuilder sb = new StringBuilder();
              for (; c > 32; c = scan()) {
                  sb.append((char) c);
              }
              return sb.toString();
          }
   
          int nextInt() throws IOException {
              int c, val = 0;
              for (c = scan(); c <= 32; c = scan());
              boolean neg = c == '-';
              if (c == '-' || c == '+') {
                  c = scan();
              }
              for (; c >= '0' && c <= '9'; c = scan()) {
                  val = (val << 3) + (val << 1) + (c & 15);
              }
              return neg ? -val : val;
          }
   
          long nextLong() throws IOException {
              int c;
              long val = 0;
              for (c = scan(); c <= 32; c = scan());
              boolean neg = c == '-';
              if (c == '-' || c == '+') {
                  c = scan();
              }
              for (; c >= '0' && c <= '9'; c = scan()) {
                  val = (val << 3) + (val << 1) + (c & 15);
              }
              return neg ? -val : val;
          }
      }
     
      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  PrintWriter out=new PrintWriter(System.out);
    static int int_max=Integer.MAX_VALUE;
    static int int_min=Integer.MIN_VALUE;
    static long long_max=Long.MAX_VALUE;
    static long long_min=Long.MIN_VALUE;
  }
  // Thank You !