题目描述：

LeetCode 737. Sentence Similarity II

Given two sentences words1, words2 (each represented as an array of strings), and a list of similar word pairs pairs, determine if two sentences are similar.

For example, words1 = ["great", "acting", "skills"] and words2 = ["fine", "drama", "talent"] are similar, if the similar word pairs are pairs = [["great", "good"], ["fine", "good"], ["acting","drama"], ["skills","talent"]].

Note that the similarity relation is transitive. For example, if "great" and "good" are similar, and "fine" and "good" are similar, then "great" and "fine" are similar.

Similarity is also symmetric. For example, "great" and "fine" being similar is the same as "fine" and "great" being similar.

Also, a word is always similar with itself. For example, the sentences words1 = ["great"], words2 = ["great"], pairs = [] are similar, even though there are no specified similar word pairs.

Finally, sentences can only be similar if they have the same number of words. So a sentence like words1 = ["great"] can never be similar to words2 = ["doubleplus","good"].

Note:

• The length of words1 and words2 will not exceed 1000.
• The length of pairs will not exceed 2000.
• The length of each pairs[i] will be 2.
• The length of each words[i] and pairs[i][j] will be in the range [1, 20].

题目大意：

给定两组单词words1和words2，以及一组相似单词对pairs，相似性可以传递，判断words1与words2中的单词是否两两相似。

解题思路：

字典 / 哈希表 + DFS / BFS

利用字典similars存储相似单词对，然后遍历words1和words2，通过DFS/BFS判断是否相似

Python代码：

class Solution(object):
    def areSentencesSimilarTwo(self, words1, words2, pairs):
        """
        :type words1: List[str]
        :type words2: List[str]
        :type pairs: List[List[str]]
        :rtype: bool
        """
        if len(words1) != len(words2): return False
        similars = collections.defaultdict(set)
        for w1, w2 in pairs:
            similars[w1].add(w2)
            similars[w2].add(w1)

        def dfs(words1, words2, visits):
            for similar in similars[words2]:
                if words1 == similar:
                    return True
                elif similar not in visits:
                    visits.add(similar)
                    if dfs(words1, similar, visits):
                        return True
            return False

        for w1, w2 in zip(words1, words2):
            if w1 != w2 and not dfs(w1, w2, set([w2])):
                return False
        return True

 

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