BAEL-3418 Check If Two Strings Are Anagrams in Java (#8139)

* BAEL-3418 Check If Two Strings Are Anagrams in Java

* BAEL-3418 Update code based on code review feedback.

* BAEL-3418 Update comments and rename constant based on code review feedback.

* Move the repository to core-java-modules/core-java-string-algorithms-3/

* BAEL-3418 Only support alpha characters for the anagram

* BAEL-3418 use preprocess in a separate method

* BAEL-3418 Remove the temp variables

core-java-modules/core-java-string-algorithms-3/src/main/java/com/baeldung/anagram/Anagram.java

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+package com.baeldung.anagram;
+
+import java.util.Arrays;
+import com.google.common.collect.HashMultiset;
+import com.google.common.collect.Multiset;
+
+public class Anagram {
+    // This definition only works for single byte encoding character set.
+    // For multibyte encoding, such as UTF-8, 16, 32 etc.,
+    // we need to increase this number so that it can contain all possible characters.
+    private static int CHARACTER_RANGE = 256;
+
+    public boolean isAnagramSort(String string1, String string2) {
+        if (string1.length() != string2.length()) {
+            return false;
+        }
+        char[] a1 = string1.toCharArray();
+        char[] a2 = string2.toCharArray();
+        Arrays.sort(a1);
+        Arrays.sort(a2);
+        return Arrays.equals(a1, a2);
+    }
+
+    public boolean isAnagramCounting(String string1, String string2) {
+        if (string1.length() != string2.length()) {
+            return false;
+        }
+        int count[] = new int[CHARACTER_RANGE];
+        for (int i = 0; i < string1.length(); i++) {
+            count[string1.charAt(i)]++;
+            count[string2.charAt(i)]--;
+        }
+        for (int i = 0; i < CHARACTER_RANGE; i++) {
+            if (count[i] != 0) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    public boolean isAnagramMultiset(String string1, String string2) {
+        if (string1.length() != string2.length()) {
+            return false;
+        }
+        Multiset<Character> multiset1 = HashMultiset.create();
+        Multiset<Character> multiset2 = HashMultiset.create();
+        for (int i = 0; i < string1.length(); i++) {
+            multiset1.add(string1.charAt(i));
+            multiset2.add(string2.charAt(i));
+        }
+        return multiset1.equals(multiset2);
+    }
+
+    public boolean isLetterBasedAnagramMultiset(String string1, String string2) {
+        return isAnagramMultiset(preprocess(string1), preprocess(string2));
+    }
+
+    private String preprocess(String source) {
+        return source.replaceAll("[^a-zA-Z]", "").toLowerCase();
+    }
+
+}

core-java-modules/core-java-string-algorithms-3/src/test/java/com/baeldung/anagram/AnagramUnitTest.java

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+package com.baeldung.anagram;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class AnagramUnitTest {
+    @Test
+    public void givenAnagram_whenUsingSort_thenIdentifyAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcab";
+        String string2 = "cabba";
+        assertTrue(anagram.isAnagramSort(string1, string2));
+    }
+
+    @Test
+    public void givenAnagram_whenUsingCounting_thenIdentifyAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcab";
+        String string2 = "cabba";
+        assertTrue(anagram.isAnagramCounting(string1, string2));
+    }
+
+    @Test
+    public void givenAnagram_whenUsingMultiset_thenIdentifyAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcab";
+        String string2 = "cabba";
+        assertTrue(anagram.isAnagramMultiset(string1, string2));
+    }
+
+    @Test
+    public void givenAnagram_whenUsingLetterBasedMultiset_thenIdentifyAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "A decimal point";
+        String string2 = "I’m a dot in place.";
+        assertTrue(anagram.isLetterBasedAnagramMultiset(string1, string2));
+    }
+
+    @Test
+    public void givenNonAnagram_whenUsingSort_thenIdentifyNotAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcaba";
+        String string2 = "cabbac";
+        assertFalse(anagram.isAnagramSort(string1, string2));
+    }
+
+    @Test
+    public void givenNonAnagram_whenUsingCounting_thenIdentifyNotAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcaba";
+        String string2 = "cabbac";
+        assertFalse(anagram.isAnagramCounting(string1, string2));
+    }
+
+    @Test
+    public void givenNonAnagram_whenUsingMultiset_thenIdentifyNotAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "abcaba";
+        String string2 = "cabbac";
+        assertFalse(anagram.isAnagramMultiset(string1, string2));
+    }
+
+    @Test
+    public void ggivenNonAnagram_whenUsingLetterBasedMultiset_thenIdentifyAnagram() {
+        Anagram anagram = new Anagram();
+        String string1 = "A decimal point";
+        String string2 = "I’m dot in place.";
+        assertFalse(anagram.isAnagramMultiset(string1, string2));
+    }
+}