LeetCode 472. Concatenated Words

Problem Statement

(Source) Given a list of words, please write a program that returns all concatenated words in the given list of words.

A concatenated word is defined as a string that is comprised entirely of at least two shorter words in the given array.

Example:

Input: ["cat","cats","catsdogcats","dog","dogcatsdog","hippopotamuses","rat","ratcatdogcat"]Output: ["catsdogcats","dogcatsdog","ratcatdogcat"]Explanation: "catsdogcats" can be concatenated by "cats", "dog" and "cats";  "dogcatsdog" can be concatenated by "dog", "cats" and "dog"; "ratcatdogcat" can be concatenated by "rat", "cat", "dog" and "cat".

Note:

1. The number of elements of the given array will not exceed 10,000
2. The length sum of elements in the given array will not exceed 600,000.
3. The returned elements order does not matter.

Solution

class Solution(object):    def findAllConcatenatedWordsInADict(self, words):        """        :type words: List[str]        :rtype: List[str]        """        st = set(words)        def helper(word):            sta = [0]            explored = {0}            n = len(word)            while sta:                left = sta.pop()                if left == n: return True                for right in xrange(left+1, n+1):                    if word[left : right] in st and right not in explored and (right != n or left > 0):                        sta.append(right)                        explored.add(right)            return False        return [word for word in words if word and helper(word)]