What Is a Trie Data Structure in Java?


Angela Bailey

A Trie data structure, also known as a prefix tree, is a tree-like data structure commonly used to store and retrieve strings efficiently. It is particularly useful when dealing with large datasets or when there is a need to search for words or prefixes quickly.

Structure of a Trie

A Trie consists of nodes, where each node represents a character in a string. The root node represents an empty string, and each subsequent level corresponds to the characters of the input strings. Each node can have multiple child nodes, representing the possible characters that can follow the current character.

Each node in the trie has two main components:

  • Value: This represents the character associated with the node.
  • Children: This is an array or a map that stores references to child nodes.


Let’s consider an example where we want to store the words “apple”, “application”, and “banana” in a Trie:

        /      \
       a        b
     / | \        \
    p  p  l        a
   /    |          \
  p     e           n
 / \    |           |
l   l   |           |
     i   t          a
    /     \         |
   c      i         n
  /       |         |
a        o          a
|        |          |
p        n          |
p        s

Operations on Trie

Tries support several operations that make them efficient for storing and searching strings:

  • Insertion: To insert a word into the Trie, we start at the root and follow the path corresponding to the characters of the word. If a node does not exist, we create a new node and insert it into the Trie. Once we reach the end of the word, we mark the last node as a leaf node to indicate that a complete word exists.
  • Search: To search for a word in the Trie, we start at the root and follow the path corresponding to the characters of the word.

    If we reach a null node before completing the word, it means that the word does not exist in the Trie.

  • Prefix Search: To find all words with a given prefix, we navigate to the last character of the prefix and perform a depth-first search from that node. Each time we encounter a leaf node during traversal, it represents a complete word with that prefix.
  • Deletion: Deleting a word from a Trie involves finding and removing its leaf node. If removing this leaf node causes its parent’s children count to become zero, we recursively delete its parent as well until reaching either another branch or root.

Benefits of Using Tries

Tries offer several advantages:

  • Efficient Search: Tries allow for quick lookups by performing search operations in O(m) time complexity, where m is the length of the string being searched.
  • Prefix Matching: Tries excel at finding all words matching a given prefix efficiently.
  • Space Efficiency: Though Tries may require more memory compared to other data structures, they optimize space by sharing common prefixes among multiple words.
  • Suitable for Autocomplete/Suggestions: Tries are often used in autocomplete or suggestion features as they allow for fast prefix matching.

Now that you understand the basic concepts and operations of a Trie data structure, you can explore its implementation in Java.

Happy coding!

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