Question

I’m implementing a trie which will store both the substrings and their number of occurrence in a string. Each node in my trie will have a Map called children, which will store any subnodes of the main node.

My problem is that eventually, those subnodes will have subnodes of their own and I don’t know how I will be able to retrieve data from “a map within a map within a map…” so to speak.

Here’s what I have so far:

private class TrieNode
{
    private T data; //will hold the substring
    int count; //how many occurrences of it were in the string
    private Map<TrieNode, Integer> children; //will hold subnodes
    private boolean isWord; //marks the end of a word if a substring is the last substring of a String

    private TrieNode(T data)
    {
        this.data = data;
        count = 1;
        children = new HashMap<TrieNode, Integer>();
        isWord = false;
    }
} 

How do I retrieve data from the subnodes, who might themselves have other subnodes beneath them?

P.S. I apologize if I wasn’t able to explain it clearly enough- I’m having problems with recursion. Thanks.

Answer 1

I don’t see why you’d store a string in a type called T. That sounds like a generic type, but you haven’t declared it on the class.

Anyway, I presume you’ll need a Map<T, TrieNode> that will hold each child keyed by its substring. That way you recur into another TrieNode, which again has another map of the same kind.