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: import java.io.*;
  import java.lang.reflect.Array;
  import java.math.RoundingMode;
  import java.text.DecimalFormat;
  import java.util.*;
  
  
  
  public class copy{
      public static int find(int a,int[] parent)
      {
          if(parent[a]==a)
              return a;
          return find(parent[a],parent);
      }
  
      public static void union(int a,int b,int[] parent, int[] rank,int[] children)
      {
          int x=find(a,parent);
          int y=find(b,parent);
          if(rank[x]>rank[y])
          {
              parent[y]=x;
              children[x]+=children[y];
          }
          else if(rank[y]>rank[x])
          {
              parent[x]=y;
              children[y]+=children[x];
          }
          else
          {
              parent[y]=x;
              rank[x]++;
              children[x]+=children[y];
          }
      }
  
      static double answer;
  
      public static int check(ArrayList<ArrayList<Integer>> edges,int x,int parent,int[] statues,int n)
      {
          ArrayList<Integer> arr=new ArrayList<>();
          for(int i:edges.get(x))
          {
              if(i!=parent)
              {
                  arr.add(check(edges,i,x,statues,n));
              }
          }
          int sum=0;
          for(int i=arr.size()-1;i>=0;i--)
          {
  
              answer+=((long)arr.get(i)*(long)sum*(long)statues[x])/((double)n*(double)(n-1));
              sum+=arr.get(i);
          }
          answer+=((long)sum*(long)statues[x])/((double)n*(double)(n-1));
          //System.out.println(x+" "+sum);
          return 1+sum;
      }
  
      public static boolean check(int X,int a,int b)
      {
          System.out.println(X);
  
          if(X==1)
              return true;
          boolean status=false;
          if(X%a==0 && a!=1)
              status=status || check(X/a,a,b);
          if(X-b>=1 && b!=0)
              status=status || check(X-b,a,b);
  
          return status;
  
  
      }
  
      public static int check(long xor,ArrayList<Long> sum,int low,int N)
      {
          int l=low;
          int r=N-1;
          while(l<=r)
          {
              int mid=(l+r)/2;
              if(sum.get(mid)==xor)
              {
                  return mid;
              }
              else
                  r=mid-1;
          }
  
          return 0;
      }
  
      public static void merge(int l,int mid,int r,cp[] arr,HashMap<Integer,Integer> before)
      {
          int N=mid-l+1,M=r-mid;
          cp[] arr1=new cp[mid-l+1];
          cp[] arr2=new cp[r-mid];
          cp[] arr3=new cp[N+M];
          for(int i=l;i<=mid;i++)
              arr1[i-l]=arr[i];
          for(int i=mid+1;i<=r;i++)
              arr2[i-mid-1]=arr[i];
          int left=0,right=0,k=0;
          while(left<N && right<M)
          {
  
              if(arr1[left].a<arr2[right].a)
              {
                  arr3[k++]=arr1[left++];
              }
              else
              {
  
                  before.put(arr2[right].b,before.getOrDefault(arr2[right].b,0)+N-left);
                  count+=N-left;
                  arr3[k++]=arr2[right++];
              }
          }
  
          while(left<N)
          {
              arr3[k++]=arr1[left++];
          }
  
          while(right<M)
          {
              arr3[k++]=arr2[right++];
          }
  
          for(int i=l;i<=r;i++)
              arr[i]=arr3[i-l];
  
  
  
      }
  
      public static void inv(HashMap<Integer,Integer> before,int l,int r,cp[] arr)
      {
          if(l==r)
              return;
          int mid=(l+r)/2;
          inv(before,l,mid,arr);
          inv(before,mid+1,r,arr);
          merge(l,mid,r,arr,before);
      }
      static long count=0;
      public static int check(ArrayList<Long> arr,long X,int low,int N,long mod)
      {
          int l=low;
          int r=N;
          while(l<=r)
          {
              int mid=l+(r-l)/2;
              if(((arr.get(mid)-arr.get(low-1)))/(long)(mid-low+1)<X)
              {
                  if(mid+1<=N &&  ((arr.get(mid+1)-arr.get(low-1)))/(long)(mid-low+2)<X)
                      l=mid+1;
                  else
                      return mid;
              }
              else
                  r=mid-1;
          }
  
          return -1;
      }
  
      public static void check(ArrayList<ArrayList<Integer>> arr,int x,int parent,ArrayList<Integer> answer)
      {
          answer.add(x);
          for(int i:arr.get(x))
          {
              if(i!=parent)
              {
                  check(arr,i,x,answer);
                  answer.add(x);
              }
          }
  
      }
  
      static long binpow( long a,  long b,  long m) {
          a %= m;
          long  res = 1;
          while (b > 0) {
              if ((b & 1)==1)
                  res = res * a % m;
              a = a * a % m;
              b >>= 1;
          }
          return res;
      }
      public static int check(int N,int a,int b,int c,int[] dp)
      {
          if(dp[N]!=-2)
              return dp[N];
          if(N==0)
              return 0;
  
          int a1=-1,a2=-1,a3=-1;
          if(N>=a)
              a1=check(N-a,a,b,c,dp);
          if(N>=b)
              a2=check(N-b,a,b,c,dp);
          if(N>=c)
              a3=check(N-c,a,b,c,dp);
          if(a1==-1 && a2==-1 && a3==-1)
              dp[N]=-1;
          else
              dp[N]= 1+Math.max(a1,Math.max(a2,a3));
          return dp[N];
      }
  
      static int curr=0;
      public static int check(ArrayList<ArrayList<Integer>> arr,int x,int parent)
      {
          int total=Integer.MIN_VALUE;
          int max1=0,max2=0;
          for(int i:arr.get(x))
          {
              if(i==parent)
                  continue;
              curr=0;
              total=Math.max(total,check(arr,i,x));
              if(curr>max1)
              {
                  max2=max1;
                  max1=curr;
              }
              else if(curr>max2)
                  max2=curr;
  
  
          }
          total=Math.max(total,max1+max2);
          curr=max1+1;
          return total;
      }
  
      public static long gcd(long a,long b)
      {
          if(a==0)
              return b;
  
          return gcd(b%a,a);
      }
  
  
      public static int check(ArrayList<Double> arr,double number,int N)
      {
          int l=0;
          int r=N;
          while(l<=r)
          {
              int mid=(l+r)/2;
              if(number>=arr.get(mid))
              {
                  if(mid+1<=N && arr.get(mid+1)<=number)
                      l=mid+1;
                  else
                      return mid;
              }
              else
                  r=mid-1;
              //System.out.println("hello");
          }
  
          return 0;
      }
  
  
      public static int check(ArrayList<String> arr)
      {
          int ans=Integer.MAX_VALUE;
          ArrayList<Character> copy=new ArrayList<>();
          for(char ch='a';ch<='z';ch++)
          {
              int s1=0;
              for(String s:arr)
                  if(s.indexOf(ch)!=-1)
                      ++s1;
                  if(s1>1)
                  {
                      copy.add(ch);
                  }
  
          }
          if(copy.size()==0) {
              for (char ch = 'a'; ch <= 'z'; ch++) {
                  int s1 = 0, s2 = 0;
                  for (String s : arr)
                      if (s.indexOf(ch) != -1)
                          s1 += s.length();
                      else
                          s2 += s.length();
  
                  //System.out.println(ch+" "+s1+" "+s2);
                  ans = Math.min(ans, Math.abs(s1 - s2));
  
              }
          }
          else
          {
              for (char ch:copy) {
                  int s1 = 0, s2 = 0;
                  for (String s : arr)
                      if (s.indexOf(ch) != -1)
                          s1 += s.length();
                      else
                          s2 += s.length();
  
                  //System.out.println(ch+" "+s1+" "+s2);
                  ans = Math.min(ans, Math.abs(s1 - s2));
  
              }
          }
  
          return ans;
      }
  
  
  
  
  
  
  
  
  
  
  
  
  
      public static void main(String[] args)throws IOException
      {
          Reader.init(System.in);
          BufferedWriter output=new BufferedWriter(new OutputStreamWriter(System.out));
          int T=Reader.nextInt();
          for(int m=1;m<=T;m++)
          {
              int N=Reader.nextInt();
              String s=Reader.next();
              int ans=0;
              char ch='R';
              for(int i=0;i<N;i++)
              {
                  if(s.charAt(i)!=ch && s.charAt(i)!='?')
                  {
                      ++ans;
                  }
                  else{
                      if(ch=='R')
                          ch='B';
                      else
                          ch='R';
                  }
              }
              int ans1=0;
              ch='B';
              for(int i=0;i<N;i++)
              {
                  if(s.charAt(i)!=ch && s.charAt(i)!='?')
                  {
                      ++ans1;
                  }
                  else{
                      if(ch=='R')
                          ch='B';
                      else
                          ch='R';
                  }
              }
              String s1="";
              if(ans<ans1)
              {
                  ch='R';
                  for(int i=0;i<N;i++)
                  {
                      if(s.charAt(i)=='?') {
                          s1 += ch;
                          if(ch=='R')
                              ch='B';
                          else
                              ch='R';
                      }
                      else if(s.charAt(i)==ch)
                      {
                          s1+=s.charAt(i);
                          if(ch=='R')
                              ch='B';
                          else
                              ch='R';
                      }
                      else
                      {
                          s1+=s.charAt(i);
                      }
                  }
              }
              else
              {
                  ch='B';
                  for(int i=0;i<N;i++)
                  {
                      if(s.charAt(i)=='?')
                      {
                          s1+=ch;
                          if(ch=='R')
                              ch='B';
                          else
                              ch='R';
                      }
                      else if(s.charAt(i)==ch)
                      {
                          s1+=s.charAt(i);
                          if(ch=='R')
                              ch='B';
                          else
                              ch='R';
                      }
                      else
                      {
                          s1+=s.charAt(i);
                      }
                  }
              }
              output.write(s1+"\n");
          }
          output.flush();
  
      }
  }
  
  class cord
  {
      int x;
      cord next;
      cord(int x)
      {
          this.x=x;
      }
  }
  
  class cp
  {
      int a,b;
      cp(int a,int b)
      {
          this.a=a;
          this.b=b;
  
      }
  }
  
  class sort_cp implements Comparator<cp>
  {
      public int compare(cp o1,cp o2)
      {
          if(o1.b>o2.b)
              return -1;
          else if(o1.b<o2.b)
              return 1;
          else
              return 0;
      }
  }
  class g_node{
      int val;
      long wt;
  
      g_node(int val, long wt)
      {
          this.val = val;
          this.wt = wt;
      }
  }
  class Reader {
      static BufferedReader reader;
      static StringTokenizer tokenizer;
  
      static void init(InputStream input) {
          reader = new BufferedReader(
                  new InputStreamReader(input));
          tokenizer = new StringTokenizer("");
      }
  
      static String next() throws IOException {
          while (!tokenizer.hasMoreTokens()) {
              tokenizer = new StringTokenizer(
                      reader.readLine());
          }
          return tokenizer.nextToken();
      }
  
      static int nextInt() throws IOException {
          return Integer.parseInt(next());
      }
  
      static long nextLong() throws IOException {
          return Long.parseLong(next());
      }
  
      static double nextDouble() throws IOException {
          return Double.parseDouble(next());
      }
  }