LeetCode 288. Unique Word Abbreviation（单词缩写）

原题网址：https://leetcode.com/problems/unique-word-abbreviation/

An abbreviation of a word follows the form <first letter><number><last letter>. Below are some examples of word abbreviations:

a) it                      --> it    (no abbreviation)

1
b) d|o|g                   --> d1g

1    1  1
1---5----0----5--8
c) i|nternationalizatio|n  --> i18n

1
1---5----0
d) l|ocalizatio|n          --> l10n

Assume you have a dictionary and given a word, find whether its abbreviation is unique in the dictionary. A word's abbreviation is unique if no other word from the dictionary has the same abbreviation.

Example:

Given dictionary = [ "deer", "door", "cake", "card" ]

isUnique("dear") -> [code]false

isUnique("cart") ->

true

isUnique("cane") ->

false

isUnique("make") ->

true

方法：比较直接的方法，就是建立哈希映射，以缩写为key，以原始的单词为value。

public class ValidWordAbbr {
private Map<String, Set<String>> abbrs = new HashMap<>();

private String abbr(String word) {
if (word.length() <= 2) return word;
StringBuilder sb = new StringBuilder();
sb.append(word.charAt(0));
sb.append(word.length()-2);
sb.append(word.charAt(word.length()-1));
return sb.toString();
}
public ValidWordAbbr(String[] dictionary) {
for(String word: dictionary) {
String abbr = abbr(word);
Set<String> words = abbrs.get(abbr);
if (words == null) {
words = new HashSet<>();
abbrs.put(abbr, words);
}
words.add(word);
}
}

public boolean isUnique(String word) {
Set<String> words = abbrs.get(abbr(word));
if (words == null || words.isEmpty()) return true;
if (words.size() == 1 && words.contains(word)) return true;
return false;
}
}

// Your ValidWordAbbr object will be instantiated and called as such:
// ValidWordAbbr vwa = new ValidWordAbbr(dictionary);
// vwa.isUnique("Word");
// vwa.isUnique("anotherWord");

方法二：可以优化不使用哈希集合。

public class ValidWordAbbr {
private Map<String, Abbr> map = new HashMap<>();

private String abbr(String word) {
if (word == null || word.length() <=2) return word;
return word.substring(0,1) + Integer.toString(word.length()-2) + word.substring(word.length()-1);
}

public ValidWordAbbr(String[] dictionary) {
for(String word: dictionary) {
String key = abbr(word);
Abbr abbr = map.get(key);
if (abbr == null) abbr = new Abbr(word);
else if (!word.equals(abbr.word)) abbr.count ++;
map.put(key, abbr);
}
}

public boolean isUnique(String word) {
Abbr abbr = map.get(abbr(word));
if (abbr == null) return true;
if (abbr.count > 1) return false;
if (abbr.word.equals(word)) return true;
return false;
}
}
class Abbr {
int count;
String word;
Abbr(String word) {
this.word = word;
this.count = 1;
}
}

// Your ValidWordAbbr object will be instantiated and called as such:
// ValidWordAbbr vwa = new ValidWordAbbr(dictionary);
// vwa.isUnique("Word");
// vwa.isUnique("anotherWord");