# C++ Trie Implementation

Tries are a lesser known, but very useful data structure. A trie (or prefix tree) is an ordered tree data structure, such that each descendant of a given node in a trie share a common prefix. This property makes for fast prefix based queries (used in auto complete, spell check, etc.).

A trie with words a, at, ate, on, one, out, my, me, and mud. Filled in nodes denote the end of a word.

Implementing a trie is similar to implementing any other n-ary tree, with a few key differences.

# The Node

Each node in a trie has a set of outgoing edges labeled by a character. Each node must also contain a flag indicating whether it is a valid word end.

Outgoing edges can be represented by a map of `char => node*`

.

`n[c] => m`

denotes that n has an outgoing edge labeled c, incident on m.

The end of word marker can be represented trivially by a boolean field.

Our node ends up looking like this:

# The Trie

As with most tree-like structures, the only data member required for a trie is a node which points to the root.

To insert into a trie, you simply iterate through the input string and walk the corresponding edge labels. If a given edge does not exist, create it. Once you have exhausted the input string, mark the node you ended on as a valid end of word.

Since tries have no cylces, we were able to use unique_ptr everywhere, and thus do not need to worry about explicity freeing any memory assoicated with our trie.