Method backtrack

FindUniqueBinaryString.java:15–31

(String nums[], int n,HashSet<String> set, StringBuilder res)

        return res.toString();
    }
    public boolean backtrack(String nums[], int n,HashSet<String> set, StringBuilder res){
        //base case
        if(res.length() == n){
            if(!set.contains(res.toString())){
                return true;
            }
            return false;
        }
        for(char ch='0';ch<='1';ch++){
            res.append(ch);
            if(backtrack(nums,n,set,res)){
                return true;
            }
            res.deleteCharAt(res.length()-1);
        }
        return false;
    }
}