diff --git a/src/main/java/Triangle.java b/src/main/java/Triangle.java
deleted file mode 100644
index c402cde..0000000
--- a/src/main/java/Triangle.java
+++ /dev/null
@@ -1,21 +0,0 @@
-public class Triangle {
-
-    private final int a;
-    private final int b;
-    private final int c;
-
-    public Triangle(int a, int b, int c) {
-        this.a = a;
-        this.b = b;
-        this.c = c;
-    }
-
-    public double calcSquare() {
-        int p = calcPerimeter();
-        return Math.sqrt(p * (p - a) * (p - b) * (p - c));
-    }
-
-    public int calcPerimeter() {
-        return a + b + c;
-    }
-}
diff --git a/src/main/java/Trie.java b/src/main/java/Trie.java
new file mode 100644
index 0000000..97f4343
--- /dev/null
+++ b/src/main/java/Trie.java
@@ -0,0 +1,138 @@
+import java.util.*;
+
+import static java.util.Objects.hash;
+
+
+public class Trie {
+    TrieNode root;
+    ArrayList<String> words;
+
+    Trie () {
+        root = new TrieNode(' ');
+        words = new ArrayList<>();
+    }
+
+    public boolean ifExist(String word) {
+        TrieNode curr = root;
+        for (char c:word.trim().toLowerCase().toCharArray()) {
+            if (curr.getChild(c) == null) return false;
+            else curr = curr.getChild(c);
+        }
+        return curr.isLastSymbol;
+    }
+
+    public void printIfExist(String word) {
+        if (ifExist(word)) System.out.printf("Слово \"%s\" найдено\n", word);
+        else System.out.printf("Слово \"%s\" не найдено\n", word);
+    }
+
+
+    public void add(String word) {
+        if (ifExist(word) || word.length() == 0) return;
+        TrieNode curr = root;
+        var chars = word.toLowerCase().toCharArray();
+        for (int i = 0; i < chars.length; i++) {
+            TrieNode child = curr.getChild(chars[i]);
+            if (child != null) curr = child;
+            else {
+                curr.children.add(new TrieNode(chars[i]));
+                curr = curr.getChild(chars[i]);
+            }
+            curr.count++;
+            curr.text = word.substring(0, i + 1);
+        }
+        curr.isLastSymbol = true;
+        words.add(word.trim().toLowerCase());
+    }
+
+    public void remove(String word) {
+        if (!ifExist(word) || word.trim().length() == 0) return;
+        TrieNode curr = root;
+        char[] chars = word.trim().toLowerCase().toCharArray();
+        for (char c : chars) {
+            TrieNode child = curr.getChild(c);
+            if (child.count == 1) {
+                curr.children.remove(child);
+                words.remove(word);
+                return;
+            } else {
+                child.count--;
+                curr = child;
+            }
+        }
+        curr.isLastSymbol = false;
+        words.remove(word.trim().toLowerCase());
+    }
+
+    public ArrayList<String> prefixSearch(String prefix) {
+        TrieNode curr = root;
+        for(char c:prefix.toLowerCase().toCharArray()) {
+            curr = curr.getChild(c);
+            if(curr == null) return null;
+        }
+        return allWords(curr);
+    }
+
+    private ArrayList<String> allWords(TrieNode node) {
+        if (node == null) return null;
+        ArrayList<String> res = new ArrayList<>();
+        if (node.isLastSymbol) res.add(node.text);
+        for (TrieNode child:node.children) {
+            res.addAll(allWords(node.getChild(child.value)));
+        }
+        return res;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null || getClass() != obj.getClass()) return false;
+        Trie t = (Trie) obj;
+        return this.words.equals(t.words);
+    }
+
+    @Override
+    public String toString() {
+        return this.words.toString();
+    }
+
+    @Override
+    public int hashCode() {
+        return hash(this.words);
+    }
+
+    public static void main(String[] args) {
+        Trie t = new Trie();
+        Trie t1 = new Trie();
+        t.add("qer");
+        t1.add("qer");
+        t1.add("qaw");
+        System.out.println(t1.words);
+        t1.remove("qaw");
+        System.out.println(t1.words);
+    }
+}
+
+class TrieNode {
+    char value;
+    ArrayList<TrieNode> children;
+    boolean isLastSymbol;
+    int count;
+    String text;
+
+    TrieNode(char value) {
+        this.value = value;
+        isLastSymbol = false;
+        children = new ArrayList<>();
+        count = 0;
+    }
+
+    public TrieNode getChild(char input) {
+        if (children != null) {
+            for (TrieNode child : children) {
+                if (child.value == input) return child;
+            }
+        }
+        return null;
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/TriangleTest.java b/src/test/java/TriangleTest.java
deleted file mode 100644
index b743089..0000000
--- a/src/test/java/TriangleTest.java
+++ /dev/null
@@ -1,13 +0,0 @@
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import org.junit.jupiter.api.Test;
-
-public class TriangleTest {
-
-    @Test
-    public void testTriangleSquare() {
-        Triangle triangle = new Triangle(1, 1, 1);
-        double expectedSquare = 5;
-        assertEquals(expectedSquare, Math.round(triangle.calcSquare()));
-    }
-}
diff --git a/src/test/java/TrieTest.java b/src/test/java/TrieTest.java
new file mode 100644
index 0000000..b9a069b
--- /dev/null
+++ b/src/test/java/TrieTest.java
@@ -0,0 +1,56 @@
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class TrieTest {
+
+    Trie trie1 = new Trie();
+    Trie trie2 = new Trie();
+
+    @Test
+    public void testIfExist() {
+        trie1.add("qq");
+        assertTrue(trie1.ifExist("qq"));
+        assertFalse(trie1.ifExist("a"));
+        assertTrue(trie1.ifExist("QQ"));
+        assertFalse(trie1.ifExist(" "));
+    }
+
+    @Test
+    public void testAdd() {
+        trie1.add("a");
+        trie1.add("aaa");
+        trie2.add("a");
+        trie2.add("  aAa   ");
+        assertEquals(trie1, trie2);
+        trie2.add("b");
+        assertNotEquals(trie1, trie2);
+    }
+
+    @Test
+    public void testRemove() {
+        trie1.add("a");
+        trie2.add("a");
+        assertEquals(trie1, trie2);
+        trie1.remove("a");
+        assertNotEquals(trie1, trie2);
+    }
+
+    @Test
+    public void testPrefixSearch() {
+        String[] resAr = {"maxwell", "mendel", "mendeleev"};
+        String[] resAr1 = {"mendel", "mendeleev"};
+        trie1.add("maxwell");
+        trie1.add("mendel");
+        trie1.add("mendeleev");
+        trie1.add("pavlov");
+        trie1.add("pasteur");
+        trie1.add("poincare");
+        trie1.add("turing");
+        assertEquals(trie1.prefixSearch("m"), List.of(resAr));
+        assertEquals(trie1.prefixSearch("men"), List.of(resAr1));
+    }
+}