added PATRICIA Trie

Author: shimmer12

src/main/java/com/thealgorithms/datastructures/tries/PatriciaTrie.java

@@ -0,0 +1,126 @@
+package com.thealgorithms.datastructures.tries;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class PatriciaTrieTest {
+
+    @Test
+    void insertAndGet_basic() {
+        var t = new PatriciaTrie<Integer>();
+        t.put("ant", 1);
+        t.put("ante", 2);
+        t.put("anti", 3);
+        assertEquals(3, t.size());
+        assertEquals(1, t.get("ant"));
+        assertEquals(2, t.get("ante"));
+        assertEquals(3, t.get("anti"));
+        assertNull(t.get("aunt"));
+    }
+
+    @Test
+    void overwriteValue_doesNotChangeSize() {
+        var t = new PatriciaTrie<String>();
+        t.put("car", "A");
+        assertEquals(1, t.size());
+        t.put("car", "B");
+        assertEquals(1, t.size());
+        assertEquals("B", t.get("car"));
+    }
+
+    @Test
+    void startsWith_variousPrefixes() {
+        var t = new PatriciaTrie<Integer>();
+        t.put("an", 1); t.put("ant", 2); t.put("anthem", 3); t.put("banana", 4);
+        assertTrue(t.startsWith("an"));
+        assertTrue(t.startsWith("ant"));
+        assertTrue(t.startsWith("anthem"));
+        assertFalse(t.startsWith("ante"));
+        assertTrue(t.startsWith("b"));
+        assertFalse(t.startsWith("c"));
+        assertTrue(t.startsWith("")); // non-empty trie => true
+    }
+
+    @Test
+    void unicodeKeys_supported() {
+        var t = new PatriciaTrie<String>();
+        t.put("mañana", "sun");
+        t.put("манго", "mango-cyrillic");
+        assertTrue(t.contains("mañana"));
+        assertTrue(t.contains("манго"));
+        assertEquals("sun", t.get("mañana"));
+        assertTrue(t.startsWith("ма")); // prefix in Cyrillic
+    }
+
+    @Test
+    void remove_leafKey() {
+        var t = new PatriciaTrie<Integer>();
+        t.put("cat", 1);
+        t.put("car", 2);
+        assertTrue(t.remove("car"));
+        assertFalse(t.contains("car"));
+        assertTrue(t.contains("cat"));
+        assertEquals(1, t.size());
+    }
+
+    @Test
+    void remove_internalCausesMerge() {
+        var t = new PatriciaTrie<Integer>();
+        t.put("card", 1);
+        t.put("care", 2);
+        t.put("car", 3);
+        // remove "car" which sits on the path to "card" and "care"
+        assertTrue(t.remove("car"));
+        assertFalse(t.contains("car"));
+        assertTrue(t.contains("card"));
+        assertTrue(t.contains("care"));
+        // structure should remain accessible after merge
+        assertEquals(2, t.size());
+        assertEquals(1, t.get("card"));
+        assertEquals(2, t.get("care"));
+    }
+
+    @Test
+    void remove_absentKey_noop() {
+        var t = new PatriciaTrie<Integer>();
+        t.put("alpha", 1);
+        assertFalse(t.remove("alphabet"));
+        assertEquals(1, t.size());
+        assertTrue(t.contains("alpha"));
+    }
+
+    @Test
+    void emptyKey_supported() {
+        var t = new PatriciaTrie<String>();
+        t.put("", "root");
+        assertTrue(t.contains(""));
+        assertEquals("root", t.get(""));
+        assertTrue(t.remove(""));
+        assertFalse(t.contains(""));
+        assertEquals(0, t.size());
+    }
+
+    @Test
+    void nullContracts() {
+        var t = new PatriciaTrie<Integer>();
+        assertThrows(IllegalArgumentException.class, () -> t.put(null, 1));
+        assertThrows(IllegalArgumentException.class, () -> t.put("a", null));
+        assertThrows(IllegalArgumentException.class, () -> t.get(null));
+        assertThrows(IllegalArgumentException.class, () -> t.contains(null));
+        assertThrows(IllegalArgumentException.class, () -> t.remove(null));
+        assertThrows(IllegalArgumentException.class, () -> t.startsWith(null));
+    }
+
+    @Test
+    void isEmptyAndSize() {
+        var t = new PatriciaTrie<Integer>();
+        assertTrue(t.isEmpty());
+        t.put("x", 10);
+        assertFalse(t.isEmpty());
+        assertEquals(1, t.size());
+        t.remove("x");
+        assertTrue(t.isEmpty());
+        assertEquals(0, t.size());
+    }
+}