Implement exercise AVL tree

avl-tree/README.md

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+# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>AVL tree exercise :muscle:
+Improve your TDD skill implementing AVL tree
+
+### Task
+**AVL tree** is a self-balancing binary search tree. You job is to implement the interface `AVLTree`
+ by practicing TDD discipline
+
+### Pre-conditions :heavy_exclamation_mark:
+You're supposed to know [The Three laws of TDD](https://github.com/bobocode-projects/tdd-exercises#the-three-laws-of-tdd),
+ be familiar with Java, TDD, AVL tree, and recursion
+
+### How to start :question:
+* Just clone the repository and start implementing `AVLTree` interface following *three laws of TDD*
+* If you don't have enough knowladge about this domain, check out the [links below](#related-materials-information_source)
+* Don't worry if you got stuck, checkout the [exercise/completed](https://github.com/bobocode-projects/tdd-exercises/tree/exercise/completed/avl-tree) branch and see the final implementation
+
+### Related materials :information_source:
+ * [Як виробити звичку писати тести? (Bobocode channel <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=20/>)](https://youtu.be/L_CiX9C51BI)
+ * [AVL tree](https://en.wikipedia.org/wiki/AVL_tree)
+ * [The Three Laws of TDD](https://www.youtube.com/watch?v=qkblc5WRn-U&t=3476s)
+

avl-tree/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<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">
+    <parent>
+        <artifactId>tdd-exercises</artifactId>
+        <groupId>com.bobocode</groupId>
+        <version>1.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>avl-tree</artifactId>
+
+
+</project>

avl-tree/src/main/java/com/bobocode/avl/AVLTree.java

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+package com.bobocode.avl;
+
+/**
+ * AVL tree should have an API that allow provides the following functionality:
+ * - insert an element and return true if it was inserted successfully
+ * - search an element and return true it element exists
+ * - get tree size
+ * - get tree height
+ * - perform in-order traversal by passing element @{@link java.util.function.Consumer} as a parameter
+ */
+public interface AVLTree {
+}

avl-tree/src/test/java/com/bobocode/avl/AVLTreeTest.java

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+package com.bobocode.avl;
+
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class AVLTreeTest {
+}

pom.xml

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         <module>stack</module>
         <module>linked-list</module>
         <module>avl-tree</module>
+        <module>avl-tree</module>
     </modules>
 
     <properties>