Shortest Word Distance II

update Sep 11,2017 14:13

LeetCode

This is a follow up of Shortest Word Distance. The only difference is now you are given the list of words and your method will be called repeatedly many times with different parameters. How would you optimize it?

Design a class which receives a list of words in the constructor, and implements a method that takes two words word1 and word2 and return the shortest distance between these two words in the list.

For example,

Assume that words = ["practice", "makes", "perfect", "coding", "makes"].

Given word1 = “coding”, word2 = “practice”, return 3.
Given word1 = "makes", word2 = "coding", return 1.

Note: You may assume that word1 does not equal to word2, and word1 and word2 are both in the list.

Basic Idea:

和前面一题类似，不同的是我们这次是先将所有词出现的index都分别存在一个 List 中，然后以 word 本身为 key，存入 hashmap。当query 的时候，还是相当于用双指针算法找两个排序数组中的最小差值。

Java Code：

    class WordDistance {
        private Map<String, List<Integer>> map;
        public WordDistance(String[] words) {
            this.map = new HashMap<>();
            for (int i = 0; i < words.length; ++i) {
                if (! map.containsKey(words[i])) map.put(words[i], new ArrayList<Integer>());
                map.get(words[i]).add(i);
            }
        }

        public int shortest(String word1, String word2) {
            List<Integer> idx1 = map.get(word1);
            List<Integer> idx2 = map.get(word2);
            int i = 0, j = 0, minDist = Integer.MAX_VALUE;
            while (i < idx1.size() && j < idx2.size()) {
                int diff = idx1.get(i) - idx2.get(j);
                minDist = Math.min(minDist, Math.abs(diff));
                if (diff > 0) j++;
                else i++;
            }
            return minDist;
        }
    }

update Dec 2, 2017 16:45

Update

更新一个Python的解法

    class WordDistance:
        # 分别把每个word的indices存入一个list，所有的list以word为key存入hashMap 
        def __init__(self, words):
            """
            :type words: List[str]
            """
            self.indices = {}
            for i in range(len(words)):
                if words[i] not in self.indices:
                    self.indices[words[i]] = [i]
                else:
                    self.indices[words[i]].append(i)

        # 从 dict 中取出两个 word 的indices list，然后就和 I 一样了
        def shortest(self, word1, word2):
            """
            :type word1: str
            :type word2: str
            :rtype: int
            """
            lst1 = self.indices[word1]
            lst2 = self.indices[word2]
            i, j = 0, 0
            minDiff = float('inf')
            while i < len(lst1) and j < len(lst2):
                diff = lst1[i] - lst2[j]
                minDiff = min(minDiff, abs(diff))
                if diff > 0: j += 1
                else: i += 1
            return minDiff
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