A Java implementation of the Trie data structure
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A java implementation of the Prefix Trie data structure.


Tries are map like ordered tree based data structures that provide fast searching of the order O(k) where k is the length of key. Read more about trie here.


This was initially built to use in my Android app, T9 App Launcher to quickly search through list of installed applications and launch them.

Public APIs

Currently there are 3 public implementations that can be chosen from.

  • MapTrie: HashMap backed trie implementation.
  • SortedTrie: TreeMap backed trie implementation which returns suggestions and value is ascending sort order.
  • T9Trie: Helper implementation to store and retrieve suggestions for T9 sequence.

Example usage

Creating a simple trie and getting suggestions.

final MapTrie<String> trie = new MapTrie<>();

trie.insert("Hello", "Hello");
trie.insert("Help", "Help");
trie.insert("Has", "Has");
trie.insert("Have", "Have");
trie.insert("Had", "Had");
trie.insert("Hadn't", "Hadn't");
// Print to stdout

The above print() call would print the tree structure like this.

└── h
    ├── e
    │   └── l
    │       ├── l
    │       │   └── o'Hello
    │       └── p'Help
    └── a
        ├── s'Has
        ├── v
        │   └── e'Have
        └── d'Had
            └── n
                └── '
                    └── t'Hadn't

Now let's try to find all the words starting with ha. Remember that, by default the keys are case insensitive.

List<String> suggestions = trie.getValueSuggestions("ha");

This will print [Has, Have, Had, Hadn't] to the console. The value is left untouched.


If you are a developer and would like to contribute please consider making a pull request. I would appreciate any criticisms with regards to code or implementation in general.


This project is licensed under Apache 2.0 license.