Breadth first search open turntable lock

problem ：

Code ：

class Solution {
    
   public int openLock(String[] deadends,String target){
    
        Set<String> deadendsSet =new HashSet<>();
        for(String str:deadends){
    
            deadendsSet.add(str);
        }
        // If “0000” In the death string , Will never arrive 
        if(deadendsSet.contains("0000"))
             return -1;
        // Initialize queue 
        Queue<String> que=new LinkedList<>();
        que.offer("0000");

        // To mark , The string that has been searched does not need to be searched again 
        Set<String> book=new HashSet<>();
        book.add("0000");

        int step=0;
        while(! que.isEmpty()){
    
            int n=que.size();
            // All strings converted from the previous step need to be verified and converted 
            for (int i = 0; i <n ; i++) {
    
                String curStr=que.peek();
                que.poll();
                if (curStr.equals(target)) return step;

                // Four digit code , Each position can be rotated once every time 
                for (int j = 0; j <4 ; j++) {
    
                    char newC1=curStr.charAt(j);
                    char newC2=curStr.charAt(j);
                    // The current position can be dialed forward or backward 
                    if (newC1=='9')
                        newC1='0';
                    else
                        ++newC1;
                    if (newC2=='0')
                        newC2='9';
                    else
                        --newC2;
                    StringBuilder newStr1=new StringBuilder(curStr);
                    StringBuilder newStr2=new StringBuilder(curStr);

                    newStr1.setCharAt(j,newC1);
                    newStr2.setCharAt(j,newC2);
                    if (! deadendsSet.contains(newStr1.toString()) && !book.contains(newStr1.toString())){
    
                        que.offer(newStr1.toString());
                        book.add(newStr1.toString());
                }
                if (!deadendsSet.contains(newStr2.toString()) && !book.contains(newStr2.toString())){
    
                         que.offer(newStr2.toString());
                          book.add(newStr2.toString());
                }
                }
            }
         step++;
        }
      return -1;
    }
}

Running results :