Combine strings of a file in java -

i need combine strings repeated in java this:

1. a
2. a b
3. a b c
4. a b d

to have this:

1. a b c
2. a b d

the problem strings read file, , file have more 10000 lines.

any efficient mode resolve this?

create tree structure has character value:

public class treenode {      public character value;      public map<character, treenode> childs;      public treenode() {          childs = new hashmap<character, treenode>();      } } 

for each string, read 1 character @ time. every time see "new" character, add root, , if not new, traverse through tree child character has been seen.

once done 1 string, move top of tree (to root) , same thing. "new" character, add child. if value exist within child, move child.

// take list of string input , output combined strings output public list<string> solution(list<string> input) {     treenode root = new treenode();     treenode current = root;     (string s : input) {         (int = 0; < s.length(); i++) {             character c = s.charat(i);             if (current.childs.containskey(c)) {                 current = current.childs.get(c);             } else {                 treenode child = new treenode();                 child.value = c;                 current.childs.put(c, child);                 current = child;             }         }         current = root;     }     // our tree should complete, bfs on tree unique strings.     // traverse tree while constructing string, once reach leaf     // add list.     return readstrings("", current, new arraylist<string>()); }  public list<string> readstrings(string s, treenode current, list<string> ret) {     s += current.value;     if (current.childs.size() > 0) {         (treenode child : current.childs.values()) {             readstrings(s, child, ret);         }     } else {         // @ leaf, add ret         if (s.length() > 0) {             ret.add(s);         }     }     return ret; }