Remove Sub-Folders from the Filesystem

class Solution { public List<String> removeSubfolders(String[] folder) { //sort on the basis of length // by this way all the subfolders will always appear after their parent folders //example: ["/ah/al/am","/ah/al"] after sorting ["/ah/al","/ah/al/am"] Arrays.sort(folder,(a,b)->a.length()-b.length()); List<String> list = new ArrayList<>(); Trie t = new Trie(); for(String s : folder){ if(t.insert(s,t)){ list.add(s); } } return list; } } class Trie{ boolean end = false; Map<String,Trie> map; public Trie(){ map = new HashMap<>(); } public boolean insert(String string, Trie root){ Trie temp = root; String str[] = string.split("/"); int i =0; for(String s : str){ if(s.equals("")) continue; if(!temp.map.containsKey(s)){ temp.map.put(s,new Trie()); } if(temp.end) return false; temp = temp.map.get(s); } temp.end = true; return true; } } 

class Solution { public List<String> removeSubfolders(String[] folder) { Arrays.sort(folder,(a,b)->a.length()-b.length()); List<String> list = new ArrayList<>(); Trie t = new Trie(); // add all the folders in trie for(String s : folder){ t.insert(s,t); } // check which folders are subfolders and don't add them in the final result list for(String s : folder){ if(t.canAdd(s,t)){ list.add(s); } } return list; } } class Trie{ boolean end = false; Map<String,Trie> map; public Trie(){ map = new HashMap<>(); } //insert public void insert(String string, Trie root){ Trie temp = root; String str[] = string.split("/"); int i =0; for(String s : str){ if(s.equals("")) continue; if(!temp.map.containsKey(s)){ temp.map.put(s,new Trie()); } temp = temp.map.get(s); } temp.end = true; } public boolean canAdd(String string, Trie root){ Trie temp = root; String str[] = string.split("/"); int i =0;//keep counter for(String s : str){ if(s.equals("")) continue; if(!temp.map.containsKey(s)){ temp.map.put(s,new Trie()); } //if i<str.length and temp.end = true it means that this must be a subfolder because it is  //present inside of a praent folder //example : parent could be /abc //subfolder could be (in this case) : /abc/pqr //so we will get temp.end= true before we are finished with all the the string in str or subfolders if(temp.end) return false; temp = temp.map.get(s); i++; } return true; } }