1 public class Solution { 2     public String simplifyPath(String path) { 3         if (path.isEmpty()) return ""; 4  5         StringBuilder builder = new StringBuilder(); 6         builder.append(‘/‘); 7         int index = 1; 8         while (index<path.length()){ 9             //get the next directory command.10             int next = index;11             while (next<path.length() && path.charAt(next)!=‘/‘) next++;12             String dir = path.substring(index,next);13             if (dir.equals(".") || dir.isEmpty()){14                 index = next+1;15                 continue;16             } else if (dir.equals("..")){17                 pathBack(builder);18             } else {19                 builder.append(dir);20                 builder.append(‘/‘);21             }22             index = next+1;23         }24 25         if (builder.length()>1 && builder.charAt(builder.length()-1)==‘/‘)26             builder.deleteCharAt(builder.length()-1);27         return builder.toString();28     }29 30     public void pathBack(StringBuilder builder){31         builder.deleteCharAt(builder.length()-1);32         while (builder.length()>0 && builder.charAt(builder.length()-1)!=‘/‘)33             builder.deleteCharAt(builder.length()-1);34         if (builder.length()==0) builder.append(‘/‘);35     }36 }