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Thread: Collect all words in a Trie with a prefix

  1. #1
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    Question Collect all words in a Trie with a prefix

    I'm trying to implement a method that will store all words in a Trie data structure in a List.
    This is my Node class:

    class Node {
        char c;
        HashMap<Character, Node> children = new HashMap<Character, Node>();
        boolean isCompleteWord;
     
        public Node(char c) {
            this.c = c;
            isCompleteWord = false;
        }
        public Node() {
        }
    }

    I am using a HashMap to store the child characters as keys and the child nodes as values. A node that completes a word will have the field isCompleteWord set to true.

    Methods to add all words to a List:

    List<String> collectWords(char c) {
        List<String> words = new ArrayList<>();
        String word = Character.toString(c);
        Node node = root.children.get(c);
        collectWordsHelper(words, node, word);
        return words;
    }
     
    void collectWordsHelper(List<String> words, Node node, String word) {
        for (char i = 'a'; i <= 'z'; i++) {
            if (node.children.containsKey(i)) {
                System.out.println(i); // prints the right letters
                Node child = node.children.get(i);
                word += i;
                if (child.isCompleteWord && !words.contains(word)) {
                    words.add(word);
                    collectWordsHelper(words, child, "");
                }
                collectWordsHelper(words, child, word);
            }
        }
    }

    Currently if I have stored in the Trie the words "beard", "bold", "brew", when I print the list of words starting with the prefix "b", I get:

    [beard, beold, beorew]

    What I was expecting

    [beard, bold, brew]

    I think I need a way for the String word to be reset whenever I have found a word, instead of the next characters being appended.

  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Collect all words in a Trie with a prefix

    Also posted at https://www.dreamincode.net/forums/t...with-a-prefix/

    Please read: The problems with cross-posting
    If you don't understand my answer, don't ignore it, ask a question.

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