Word Distance I – Only called once

Given a list of words and two words word1 and word2, 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.

Solution: One pass. O(n), Every time find an occurrence of word1 or word2, compare the distance of p1 and p2.

public int shortestDistance(String[] words, String word1, String word2) {
        int p1 = -1, p2 = -1, min = Integer.MAX_VALUE;
    
        for (int i = 0; i < words.length; i++) {
            if (words[i].equals(word1)) 
                p1 = i;
    
            if (words[i].equals(word2)) 
                p2 = i;
    
            if (p1 != -1 && p2 != -1)
                min = Math.min(min, Math.abs(p1 - p2));
        }
    
        return min;
    }

Shortest Word Distance II – API, will be called multiple times

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.

Solution: First preprocess the word to dict, which is a <word, list of index>map.

Then every time just get the word only check two list of indexes.

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

    public int shortest(String word1, String word2) {
        if(dict==null||!dict.containsKey(word1)||!dict.containsKey(word2)){
            return 0;
        }
        int res = Integer.MAX_VALUE;
        List<Integer> indexes1 = dict.get(word1);
        List<Integer> indexes2 = dict.get(word2);
        int index1 = 0;
        int index2 = 0;
        while(index1<indexes1.size()&&index2<indexes2.size()){
            res = Math.min(res, Math.abs(indexes1.get(index1)-indexes2.get(index2)));
            if(indexes1.get(index1)<indexes2.get(index2)){
                index1++;
            }else{
                index2++;
            }
        }
        return res;
        
    }
}

Shortest Word Distance III – word1 could be the same as word2

This is a follow up of Shortest Word Distance. The only difference is now word1 could be the same as word2.

Given a list of words and two words word1 and word2, return the shortest distance between these two words in the list.

word1 and word2 may be the same and they represent two individual words in the list.

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

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

Note:
You may assume word1 and word2 are both in the list.

Solution: if word1==word2==words[], then p1=p2=i, and every time we update p1, we check the distance between p1 and p2.

public int shortestWordDistance(String[] words, String word1, String word2) {
    int p1 = -1, p2 = -1, min = Integer.MAX_VALUE;

    for (int i = 0; i < words.length; i++) {
        if (words[i].equals(word1)) {
            p1 = i;
            if (word1.equals(word2) && p1 != -1 && p2 != -1) {
                min = Math.min(min, Math.abs(p1 - p2));
            }
        }

        if (words[i].equals(word2)) {
            p2 = i;
        }

        if (!word1.equals(word2) && p1 != -1 && p2 != -1) {
            min = Math.min(min, Math.abs(p1 - p2));
        }
    }

    return min;
}

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