Find smallest subset prefixes (part 2)

Question

Here is my code for this problem. Any bugs, performance in terms of algorithm time complexity, code style advice are appreciated.

This is a continued discussion from (Find smallest subset prefixes) and since it is new code, I post a new thread.

Problem:

Given a set of strings, return the smallest subset that contains the longest possible prefixes for every string.

If the list is ['foo', 'foog', 'food', 'asdf'] return ['foo', 'asdf']

The return is foo since foo is prefix for foo (itself), prefix for foog and prefix for food (in other words, foo could "represent" longer string like foog and food). Output also contains asdf because it is not prefix for any other words in the input list, so output itself.

The empty set is not a correct answer because it does not contain the longest possible prefixes.

Source code:

from collections import defaultdict
class TrieNode:
    def __init__(self):
        self.children = defaultdict(TrieNode)
        self.isEnd = False
    def insert(self, word):
        node = self
        for w in word:
            node = node.children[w]
        node.isEnd = True
    def find_prefix(self, prefix, result):
        if self.isEnd:
            result.append(''.join(prefix[:]))
            return
        for w, child_node in self.children.items():
            prefix.append(w)
            child_node.find_prefix(prefix, result)
            prefix.pop(-1)

if __name__ == "__main__":
    words = ['foo', 'foog', 'food', 'asdf']
    root = TrieNode()
    for w in words:
        root.insert(w)
    result = []
    root.find_prefix([], result)
    print result

Answer 1

PEP 8

You still haven't followed PEP 8. Please:

• Install (for example) Pylint.
• You can run it as pylint filename.py.
• If you use Vim you can install syntastic and every time you save it will run either flake8 or pylint.
• There are alternatives for other text editors please install one, it will save you time in the long run.

def main

You have used if __name__ == "__main__": which is good. It is even considered more idiomatic (see this answer under "An Even Better Way") to do this:

def main():
    words = ('foo', 'foog', 'food', 'asdf')
    root = TrieNode()
    for w in words:
        root.insert(w)
    result = []
    root.find_prefix([], result)
    print result

if __name__ == "__main__":
    main()

Immutability

You don't mutate words. I would turn it into a tuple.