diff --git a/hw_03/pom.xml b/hw_03/pom.xml
new file mode 100644
index 0000000..307b47f
--- /dev/null
+++ b/hw_03/pom.xml
@@ -0,0 +1,27 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>1</groupId>
+  <artifactId>hw_01</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <name>hw_01</name>
+  <url>http://maven.apache.org</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <source>1.8</source>
+    <target>1.8</target>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>3.8.1</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>
diff --git a/hw_03/src/main/java/hw_01/Bor.java b/hw_03/src/main/java/hw_01/Bor.java
new file mode 100644
index 0000000..d5a4a3a
--- /dev/null
+++ b/hw_03/src/main/java/hw_01/Bor.java
@@ -0,0 +1,145 @@
+package hw_01;
+
+import java.io.*;
+
+public class Bor implements Trie, StreamSerializable {
+	final private Node bor;
+
+	public Bor() {
+		bor = new Node();
+	}
+
+	public boolean add(String element) {
+		if (contains(element)) {
+			return false;
+		}
+		
+		Node p = bor;
+		
+		p.nwords++;
+		for (int i = 0; i < element.length(); i++) {
+			int currIdx = arrayIndex(element.charAt(i));
+			
+			if (p.lifes[currIdx] == null) {
+				p.lifes[currIdx] = new Node();
+			}
+			p = p.lifes[currIdx];
+			p.nwords++;
+		}
+		
+		p.isTerminal = true;
+		return true;
+	}
+
+	public boolean contains(String element) {
+		Node p = bor;
+		for (int i = 0; i < element.length(); i++) {
+			int currIdx = arrayIndex(element.charAt(i));
+
+			if (p.lifes[currIdx] == null) {
+				return false;
+			}
+			p = p.lifes[currIdx];
+		}
+	
+		return p.isTerminal;
+	}
+
+	public boolean remove(String element) {
+		if (!contains(element)) {
+			return false;
+		}
+		
+		Node p = bor;
+		p.nwords--;
+		for (int i = 0; i < element.length(); i++) {
+			int currIdx = arrayIndex(element.charAt(i));
+			
+			if (p.lifes[currIdx].nwords == 1) {
+				p.lifes[currIdx] = null;
+				return true;
+			}
+			p = p.lifes[currIdx];
+			p.nwords--;
+		}
+		
+		p.isTerminal = false;
+		
+		return true;
+	}
+
+	public int size() {
+		return bor.nwords;
+	}
+
+	public int howManyStartsWithPrefix(String prefix) {
+		Node p = bor;
+		for (int i = 0; i < prefix.length(); i++) {
+			int currIdx = arrayIndex(prefix.charAt(i));
+			
+			if (p.lifes[currIdx] == null) {
+				return 0;
+			}
+			p = p.lifes[currIdx];
+		}
+		
+		return p.nwords;
+	}
+
+	private int arrayIndex(char a) {
+		if ('a' <= a && a <= 'z') {
+			return a - 'a';
+		}
+		
+		if ('A' <= a && a <= 'Z') {
+			return a - 'A' + 'z' - 'a' + 1;
+		}
+		
+		return -1;
+	}
+
+	private class Node {
+		public boolean isTerminal;
+		public int nwords;
+		Node[] lifes = new Node[2*('z' - 'a' + 1)];
+	}
+	
+	private void serializeNode(Node r, DataOutputStream dos) throws IOException {
+		dos.writeBoolean(r.isTerminal);
+		dos.writeInt(r.nwords);
+		
+		for(int i = 0; i < r.lifes.length; i++) {
+			if (r.lifes[i] == null) {
+				dos.writeBoolean(false);
+			} else {
+				dos.writeBoolean(true);
+				serializeNode(r.lifes[i], dos);
+			}
+		}
+		
+	}
+	
+	private void deserializeNode(Node r, DataInputStream dis) throws IOException {
+		r.isTerminal = dis.readBoolean();
+		r.nwords = dis.readInt();
+		
+		for(int i = 0; i < r.lifes.length; i++) {
+			boolean b = dis.readBoolean();
+			if (b) {
+				r.lifes[i] = new Node();
+				deserializeNode(r.lifes[i], dis);
+			}
+		}
+	}
+	
+	@Override
+	public void serialize(OutputStream out) throws IOException {
+		serializeNode(bor, new DataOutputStream(out));
+		out.flush();
+	}
+
+	@Override
+	public void deserialize(InputStream in) throws IOException {
+		deserializeNode(bor, new DataInputStream(in));;
+	}
+}
diff --git a/hw_03/src/main/java/hw_01/StreamSerializable.java b/hw_03/src/main/java/hw_01/StreamSerializable.java
new file mode 100644
index 0000000..e9cb9df
--- /dev/null
+++ b/hw_03/src/main/java/hw_01/StreamSerializable.java
@@ -0,0 +1,15 @@
+package hw_01;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+public interface StreamSerializable {
+
+    void serialize(OutputStream out) throws IOException;
+
+    /**
+     * Replace current state with data from input stream
+     */
+    void deserialize(InputStream in) throws IOException;
+}
\ No newline at end of file
diff --git a/hw_03/src/main/java/hw_01/Trie.java b/hw_03/src/main/java/hw_01/Trie.java
new file mode 100644
index 0000000..5c043b4
--- /dev/null
+++ b/hw_03/src/main/java/hw_01/Trie.java
@@ -0,0 +1,32 @@
+package hw_01;
+
+public interface Trie {
+	 
+    /**
+     * Expected complexity: O(|element|)
+     * @return <tt>true</tt> if this set did not already contain the specified
+     *         element
+     */
+    boolean add(String element);
+ 
+    /**
+     * Expected complexity: O(|element|)
+     */
+    boolean contains(String element);
+ 
+    /**
+     * Expected complexity: O(|element|)
+     * @return <tt>true</tt> if this set contained the specified element
+     */
+    boolean remove(String element);
+ 
+    /**
+     * Expected complexity: O(1)
+     */
+    int size();
+ 
+    /**
+     * Expected complexity: O(|prefix|)
+     */
+    int howManyStartsWithPrefix(String prefix);
+}
diff --git a/hw_03/src/test/java/hw_01/TrieImplTest.java b/hw_03/src/test/java/hw_01/TrieImplTest.java
new file mode 100644
index 0000000..20fd175
--- /dev/null
+++ b/hw_03/src/test/java/hw_01/TrieImplTest.java
@@ -0,0 +1,78 @@
+package hw_01;
+
+import java.io.*;
+
+import junit.framework.TestCase;
+
+public class TrieImplTest extends TestCase {
+	private Bor b;
+
+	public void setUp() {
+		b = new Bor();
+	}
+
+	public void testAddSizeContains() {
+		assertFalse(b.contains("Hello"));
+		assertTrue(b.add("Hello"));
+		assertTrue(b.contains("Hello"));
+		assertEquals(1, b.size());
+		assertEquals(1, b.howManyStartsWithPrefix("Hell"));
+	}
+
+	public void testAddContainsPrefix() {
+		b.add("Hello");
+		assertFalse(b.contains("Hell"));
+		assertTrue(b.add("Hell"));
+		assertTrue(b.contains("Hell"));
+		assertEquals(2, b.size());
+		assertEquals(2, b.howManyStartsWithPrefix("Hell"));
+	}
+
+	public void testAddOutstandingWord() {
+		b.add("Hello");
+		assertTrue(b.add("Head"));
+		assertEquals(2, b.size());
+	}
+
+	public void testRemovePrefix() {
+		b.add("Hello");
+		b.add("Hell");
+		assertFalse(b.remove("He"));
+		assertTrue(b.remove("Hell"));
+		assertEquals(1, b.size());
+		assertEquals(1, b.howManyStartsWithPrefix("Hell"));
+	}
+
+	public void testTemoveSuffix() {
+		b.add("Hello");
+		b.add("Hell");
+		assertTrue(b.remove("Hello"));
+		assertEquals(1, b.size());
+	}
+	
+	public void testSerialDeserial() throws IOException {
+		b.add("Hello");
+		b.add("Head");
+		
+		ByteArrayOutputStream baos = new ByteArrayOutputStream();
+		b.serialize(baos);
+		byte[] buf1 = baos.toByteArray();
+		
+		Bor b1 = new Bor();
+		b1.deserialize(new ByteArrayInputStream(buf1));
+		baos = new ByteArrayOutputStream();
+		b1.serialize(baos);
+		byte[] buf2 = baos.toByteArray();
+		
+		assertEquals(buf1.length, buf2.length);
+		
+		for(int i = 0; i < buf1.length; i++) {
+			assertEquals(buf1[i], buf2[i]);
+		}
+		
+		assertTrue(b1.contains("Hello"));
+		assertTrue(b1.contains("Head"));
+		assertEquals(2, b1.size());
+	}
+
+}