Merge pull request #1163 from Zhiyuan-Amos/simplify

Simplify model answers #1119

exercises/acronym/.meta/src/reference/java/Acronym.java

-import java.util.regex.Matcher;
-import java.util.regex.Pattern;
+import java.util.Arrays;
+import java.util.stream.Collectors;
 
 final class Acronym {
 
         return acronym;
     }
 
-    private String generateAcronym(String phrase){
-        final Pattern BREAK_WORDS = Pattern.compile("[A-Z]+[a-z]*|[a-z]+");
-        final Matcher matcher = BREAK_WORDS.matcher(phrase);
-        final StringBuilder stringBuilder = new StringBuilder();
-        while (matcher.find()){
-            stringBuilder.append(matcher.group().charAt(0));
-        }
-        return stringBuilder.toString().toUpperCase();
+    private String generateAcronym(String phrase) {
+        return Arrays.stream(phrase.split("[^a-zA-Z]"))
+                .filter(word -> !word.isEmpty()) // Remove empty strings from the result of phrase.split
+                .map(word -> word.substring(0, 1)) // Get the first character of each word
+                .collect(Collectors.joining()) // Concatenate the characters
+                .toUpperCase();
     }
 
 }

exercises/anagram/.meta/src/reference/java/Anagram.java

 import java.util.*;
+import java.util.stream.Collectors;
 
 class Anagram {
 
     }
 
     List<String> match(List<String> candidates) {
-        List<String> anagrams = new ArrayList<String>();
-
-        for (String candidate : candidates) {
-            if (anagramSubject.anagramOf(candidate)) {
-                anagrams.add(candidate);
-            }
-        }
-
-        return anagrams;
+        return candidates.stream()
+                .filter(anagramSubject::anagramOf)
+                .collect(Collectors.toList());
     }
 
     static final class AnagramSubject {

exercises/atbash-cipher/.meta/src/reference/java/Atbash.java

     }
 
     private String stripInvalidCharacters(String input) {
-        StringBuilder filteredValue = new StringBuilder(input.length());
-
-        for (char c : input.toCharArray()) {
-            if (Character.isLetterOrDigit(c)) {
-                filteredValue.append(c);
-            }
-        }
-
-        return filteredValue.toString();
+        return input.replaceAll("\\W", "");
     }
 
     private char applyCipher(char input) {
         List<String> words = new ArrayList<>();
 
         for (int i = 0; i < value.length(); i += GROUP_SIZE) {
-            words.add(i + GROUP_SIZE <= value.length() ? value.substring(i, i + GROUP_SIZE) : value.substring(i));
+            words.add(value.substring(i, Math.min(value.length(), i + GROUP_SIZE)));
         }
 
         return String.join(" ", words);