CODEWITHSUNDEEP
pythonalgorithmtrie
user3699999
user3699999

Reputation: 151

Find Compound Words in List of Words using Trie

Given a list of words, I am trying to figure out how to find words in that list that are made up of other words in the list. For example, if the list were ["race", "racecar", "car"], I would want to return ["racecar"].

Here is my general thought process. I understand that using a trie would be good for this sort of problem. For each word, I can find all of its prefixes (that are also words in the list) using the trie. Then for each prefix, I can check to see if the word's suffix is made up of one or more words in the trie. However, I am having a hard time implementing this. I have been able to implement the trie and and the function to get all prefixes of a word. I am just stuck on implementing the compound word detection.

Upvotes: 0

Views: 2842

Answers (1)

niemmi
niemmi

Reputation: 17263

You could present Trie nodes as defaultdict objects which have been extended to contain a boolean flag marking if the prefix is a word. Then you could have two pass processing where on the first round you add all the words to Trie and on second round check for each word if it's a combination or not:

from collections import defaultdict

class Node(defaultdict):
    def __init__(self):
        super().__init__(Node)
        self.terminal = False

class Trie():
    def __init__(self, it):
        self.root = Node()
        for word in it:
            self.add_word(word)

    def __contains__(self, word):
        node = self.root
        for c in word:
            node = node.get(c)
            if node is None:
                return False

        return node.terminal

    def add_word(self, word):
        node = self.root
        for c in word:
            node = node[c]

        node.terminal = True

    def is_combination(self, word):
        node = self.root
        for i, c in enumerate(word):
            node = node.get(c)
            if not node:
                break
            # If prefix is a word check if suffix can be found
            if node.terminal and word[i+1:] in self:
                return True

        return False

lst = ["race", "racecar", "car"]
t = Trie(lst)

print([w for w in lst if t.is_combination(w)])

Output:

['racecar']

Upvotes: 2

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