diff --git a/src/main/java/ru/spbau/mit/StringSetImpl.java b/src/main/java/ru/spbau/mit/StringSetImpl.java
new file mode 100644
index 0000000..caf1b83
--- /dev/null
+++ b/src/main/java/ru/spbau/mit/StringSetImpl.java
@@ -0,0 +1,144 @@
+package ru.spbau.mit;
+
+public class StringSetImpl implements StringSet {
+
+    private int size;
+    private Node root;
+
+    StringSetImpl() {
+        root = new Node('a');
+    }
+
+    @Override
+    public boolean add(String element) {
+
+        if (contains(element)) {
+            return false;
+        }
+
+        Node node = root;
+        for (char value : element.toCharArray()) {
+            Node child = node.getChild(value);
+            if (child == null) {
+                child = new Node(value);
+                child.parent = node;
+                node.addChild(child);
+
+            }
+            node.howManyStartsWithPrefix++;
+            node = child;
+        }
+
+        node.isFullWord = true;
+        node.howManyStartsWithPrefix++;
+        size++;
+
+        return true;
+
+    }
+
+    private Node findLastNode(String element) {
+
+        Node node = root;
+        for (char value : element.toCharArray()) {
+            Node child = node.getChild(value);
+            if (child == null) {
+                return null;
+            }
+            node = child;
+        }
+
+        return node;
+
+    }
+
+    @Override
+    public boolean contains(String element) {
+
+        Node node = findLastNode(element);
+
+        return node != null && node.isFullWord;
+    }
+
+    private int getIndexByChar(char value) {
+        final int asciiOffset = 65;
+        return value - asciiOffset;
+    }
+
+    @Override
+    public boolean remove(String element) {
+
+        if (!contains(element)) {
+            return false;
+        }
+
+        Node lastNode = findLastNode(element);
+        lastNode.isFullWord = false;
+        lastNode.howManyStartsWithPrefix--;
+        size--;
+
+        char[] array = element.toCharArray();
+        Node parent = lastNode.parent;
+
+        // decrement value on path to root
+        for (int i = element.length() - 1; i >= 0; i--) {
+            parent.howManyStartsWithPrefix--;
+            parent = parent.parent;
+        }
+
+        // delete unused prefix
+        if (lastNode.numberOfChildren == 0) {
+            parent = lastNode.parent;
+            for (int i = element.length() - 1; i >= 0; i--) {
+                parent.numberOfChildren--;
+                parent.children[getIndexByChar(array[i])] = null;
+                if (parent.isFullWord || parent.numberOfChildren > 0) {
+                    break;
+                }
+                parent = parent.parent;
+            }
+        }
+
+        return true;
+    }
+
+    @Override
+    public int size() {
+        return size;
+    }
+
+    @Override
+    public int howManyStartsWithPrefix(String prefix) {
+        Node lastNode = findLastNode(prefix);
+        if (lastNode == null) {
+            return 0;
+        }
+        return lastNode.howManyStartsWithPrefix;
+    }
+
+    class Node {
+
+        private Node[] children;
+        private char value;
+        private int numberOfChildren;
+        private int howManyStartsWithPrefix;
+        private boolean isFullWord;
+        private Node parent;
+
+
+        Node(char value) {
+            final int sizeOfFrameInAscii = 58;
+            this.value = value;
+            this.children = new Node[sizeOfFrameInAscii];
+        }
+
+        Node getChild(char value) {
+            return children[getIndexByChar(value)];
+        }
+
+        void addChild(final Node newChild) {
+            children[getIndexByChar(newChild.value)] = newChild;
+            numberOfChildren++;
+        }
+    }
+}
diff --git a/src/test/java/ru/spbau/mit/StringSetTest.java b/src/test/java/ru/spbau/mit/StringSetTest.java
index 4eee756..f558ab4 100644
--- a/src/test/java/ru/spbau/mit/StringSetTest.java
+++ b/src/test/java/ru/spbau/mit/StringSetTest.java
@@ -15,11 +15,141 @@ public void testSimple() {
         assertTrue(stringSet.contains("abc"));
         assertEquals(1, stringSet.size());
         assertEquals(1, stringSet.howManyStartsWithPrefix("abc"));
+        assertTrue(stringSet.remove("abc"));
+        assertTrue(!stringSet.contains("abc"));
     }
 
+    @Test
+    public void moreGeneralTest() {
+        StringSet stringSet = instance();
+
+        assertTrue(stringSet.add("A"));
+        assertTrue(stringSet.add("in"));
+        assertTrue(stringSet.add("inn"));
+        assertTrue(stringSet.add("to"));
+        assertTrue(stringSet.add("tea"));
+        assertTrue(stringSet.add("ted"));
+        assertTrue(stringSet.add("ten"));
+
+        assertTrue(stringSet.contains("A"));
+        assertTrue(stringSet.contains("to"));
+        assertTrue(stringSet.contains("tea"));
+        assertTrue(stringSet.contains("ted"));
+        assertTrue(stringSet.contains("ten"));
+        assertTrue(stringSet.contains("inn"));
+        assertTrue(stringSet.contains("in"));
+
+        final int size = 7;
+        assertTrue(stringSet.size() == size);
+
+        assertTrue(stringSet.howManyStartsWithPrefix("i") == 2);
+        assertTrue(stringSet.howManyStartsWithPrefix("in") == 2);
+        assertTrue(stringSet.howManyStartsWithPrefix("te")
+                == size - (size / 2) - 1); // :)
+
+        assertTrue(stringSet.remove("in"));
+
+        assertTrue(stringSet.size() == size - 1);
+        assertTrue(!stringSet.contains("in"));
+        assertTrue(stringSet.contains("inn"));
+        assertTrue(stringSet.howManyStartsWithPrefix("in") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("te")
+                == size - (size / 2) - 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("tea") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("ted") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("ten") == 1);
+
+        assertTrue(!stringSet.remove("te"));
+        assertTrue(stringSet.size() == size - 1);
+
+        assertTrue(stringSet.howManyStartsWithPrefix("te")
+                == size - (size / 2) - 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("tea") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("ted") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("ten") == 1);
+
+        assertTrue(stringSet.remove("tea"));
+        assertTrue(stringSet.size() == size - 2);
+
+        assertTrue(stringSet.howManyStartsWithPrefix("te") == 2);
+        assertTrue(stringSet.howManyStartsWithPrefix("tea") == 0);
+        assertTrue(stringSet.howManyStartsWithPrefix("ted") == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("ten") == 1);
+
+    }
+
+    @Test
+    public void addContainsSizeRemoveSizeContains() {
+        StringSet stringSet = instance();
+
+        stringSet.add("abc");
+        stringSet.add("abd");
+        stringSet.add("bcd");
+
+        assertTrue(stringSet.contains("abc"));
+        assertTrue(stringSet.size() == 1 + 1 + 1);
+        assertTrue(stringSet.remove("abc"));
+        assertTrue(stringSet.size() == 2);
+        assertTrue(!stringSet.contains("abc"));
+    }
+
+    @Test
+    public void addContainsPrefixRemovePrefix() {
+        StringSet stringSet = instance();
+
+        stringSet.add("abc");
+        stringSet.add("abd");
+        stringSet.add("bcd");
+
+        assertTrue(stringSet.contains("abc"));
+        assertTrue(stringSet.howManyStartsWithPrefix("a") == 2);
+        assertTrue(stringSet.remove("abc"));
+        assertTrue(stringSet.howManyStartsWithPrefix("a") == 1);
+    }
+
+    @Test
+    public void doubleAdd() {
+        StringSet stringSet = instance();
+        stringSet.add("helloWorldAndVeryLongStringAfter");
+        stringSet.add("helloWorldAndVeryLongStringAfter");
+        assertTrue(stringSet.size() == 1);
+        assertTrue(stringSet.howManyStartsWithPrefix("helloWorld") == 1);
+    }
+
+    @Test
+    public void doubleDelete() {
+        StringSet stringSet = instance();
+        stringSet.add("helloWorldAndVeryLongStringAfter");
+
+        assertTrue(stringSet.remove("helloWorldAndVeryLongStringAfter"));
+        assertTrue(!stringSet.remove("helloWorldAndVeryLongStringAfter"));
+
+        assertTrue(stringSet.size() == 0);
+        assertTrue(stringSet.howManyStartsWithPrefix("helloWorld") == 0);
+    }
+
+    @Test
+    public void emptyStringsTest() {
+        StringSet stringSet = instance();
+
+        stringSet.add("abc");
+        assertTrue(stringSet.howManyStartsWithPrefix("") == 1);
+        assertTrue(stringSet.add(""));
+        assertTrue(stringSet.howManyStartsWithPrefix("") == 2);
+        assertTrue(!stringSet.add(""));
+        assertTrue(stringSet.howManyStartsWithPrefix("") == 2);
+        assertTrue(stringSet.size() == 2);
+        assertTrue(stringSet.remove(""));
+        assertTrue(stringSet.size() == 1);
+        assertTrue(stringSet.contains("abc"));
+    }
+
+
+
     public static StringSet instance() {
         try {
-            return (StringSet) Class.forName("ru.spbau.mit.StringSetImpl").newInstance();
+            return (StringSet) Class.forName("ru.spbau.mit.StringSetImpl")
+                    .newInstance();
         } catch (InstantiationException e) {
             e.printStackTrace();
         } catch (IllegalAccessException e) {