Adding solution for "Find the Anagrams" interview question

.gitignore

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+.idea
+*.iml
+out

src/techinterview/Anagram.java

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+package techinterview;
+
+import java.util.*;
+import java.util.ArrayList;
+
+/**
+ * Anagram Interview Question:
+ *
+ *    Typically posed as follows:
+ *
+ *        Given a word, and a "dictionary" find all anagrams of the given word (i.e. words which use all the same letters
+ *        as the given word but in a different order.)
+ */
+public class Anagram {
+    private Map<String, Collection<String>> anagramsByKey = new HashMap<>();
+
+    public Collection<String> findAll(String word, Collection<String> dictionary) {
+        preprocess(word, dictionary);
+
+        Collection<String> anagrams = anagramsByKey.get(generateKey(word));
+
+        if (anagrams == null) {
+            anagrams = new HashSet<>();
+        }
+
+        return anagrams;
+    }
+
+    private void preprocess(String word, Collection<String> dictionary) {
+        dictionary.stream().filter(entry -> !word.equals(entry)).forEach(entry -> {
+            String key = generateKey(entry);
+
+            if (!anagramsByKey.containsKey(key)) {
+                anagramsByKey.put(key, new HashSet<>());
+            }
+
+            anagramsByKey.get(key).add(entry);
+        });
+    }
+
+    private String generateKey(String entry) {
+        List<Character> characters = new ArrayList<>();
+
+        for (char c : entry.toCharArray()) {
+            characters.add(c);
+        }
+
+        Collections.sort(characters);
+
+        StringBuilder keySb = new StringBuilder();
+        characters.forEach(keySb::append);
+
+        return keySb.toString();
+    }
+
+}

src/TechInterview/ArrayList.java → src/techinterview/ArrayList.java

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-package TechInterview;
+package techinterview;
 
 import java.util.Arrays;
 

src/TechInterview/BinarySearch.java → src/techinterview/BinarySearch.java

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-package TechInterview;
+package techinterview;
 
 public class BinarySearch {
 

src/TechInterview/BinarySearchTree.java → src/techinterview/BinarySearchTree.java

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-package TechInterview;
+package techinterview;
 
 import java.util.LinkedList;
 import java.util.Queue;
-import java.util.Stack;
 
 public class BinarySearchTree {
 

src/TechInterview/DoublyLinkedList.java → src/techinterview/DoublyLinkedList.java

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-package TechInterview;
+package techinterview;
 
 public class DoublyLinkedList<E> {
 

src/TechInterview/HashTable.java → src/techinterview/HashTable.java

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-package TechInterview;
+package techinterview;
 
 public class HashTable {
 

src/TechInterview/MergeSort.java → src/techinterview/MergeSort.java

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-package TechInterview;
+package techinterview;
 
 import java.util.Arrays;
 

src/techinterview/Palindrome.java

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+package techinterview;
+
+public class Palindrome {
+    public static boolean is(String word) {
+        if (word == null) {
+            throw new IllegalArgumentException("Invalid argument 'null'.");
+        }
+
+        int i = 0, j = word.length() - 1;
+
+        while (i <= j) {
+            if (word.charAt(i) != word.charAt(j)) {
+                return false;
+            }
+
+            ++i;
+            --j;
+        }
+
+        return true;
+    }
+}

src/TechInterview/Queue.java → src/techinterview/Queue.java

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-package TechInterview;
+package techinterview;
 
 public class Queue<E> {
 

src/TechInterview/QuickSort.java → src/techinterview/QuickSort.java

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-package TechInterview;
+package techinterview;
 
 import java.util.Arrays;
 

src/TechInterview/SingletonDesign.java → src/techinterview/SingletonDesign.java

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-package TechInterview;
+package techinterview;
 
 public class SingletonDesign {
 

src/TechInterview/SinglyLinkedList.java → src/techinterview/SinglyLinkedList.java

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-package TechInterview;
+package techinterview;
 
 public class SinglyLinkedList<E> {
 

src/TechInterview/StackArray.java → src/techinterview/StackArray.java

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-package TechInterview;
+package techinterview;
 
 public class StackArray {
 

src/TechInterview/StackLinkedList.java → src/techinterview/StackLinkedList.java

@@ -1,4 +1,4 @@
-package TechInterview;
+package techinterview;
 
 public class StackLinkedList<E> {
 

src/TechInterview/Test.java → src/techinterview/Test.java

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-package TechInterview;
+package techinterview;
 
 public class Test {
 

src/TechInterview/Trie.java → src/techinterview/Trie.java

@@ -1,4 +1,4 @@
-package TechInterview;
+package techinterview;
 
 import java.util.HashMap;
 

src/TechInterview/Vector.java → src/techinterview/Vector.java

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-package TechInterview;
+package techinterview;
 
 import java.util.Arrays;
 

test/src/techinterview/AnagramTest.java

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+package techinterview;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+
+import static org.junit.Assert.assertEquals;
+
+public class AnagramTest {
+
+    @Test
+    public void testFindsAnagrams() throws Exception {
+        Collection<String> anagrams = new Anagram().findAll("baste", Arrays.asList("abets", "baste", "betas", "beast", "beats"));
+        assertEquals(4, anagrams.size());
+    }
+
+    @Test
+    public void testEmptyDictionaryFindsNoAnagrams() throws Exception {
+        Collection<String> anagrams = new Anagram().findAll("baste", Collections.emptyList());
+        assertEquals(0, anagrams.size());
+    }
+}

test/src/techinterview/PalindromeTest.java

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+package techinterview;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class PalindromeTest {
+
+    @Test
+    public void testIsPalindrome() throws Exception {
+        assertTrue(Palindrome.is("racecar"));
+        assertFalse(Palindrome.is("race"));
+        assertTrue(Palindrome.is("mom"));
+    }
+
+    @Test
+    public void testEmptyStringIsPalindrome() throws Exception {
+        assertTrue(Palindrome.is(""));
+    }
+
+    @Test
+    public void testSingleLetterIsPalindrome() throws Exception {
+        assertTrue(Palindrome.is("a"));
+    }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void testNullThrowsIllegalArgumentException() throws Exception {
+        Palindrome.is(null);
+    }
+}