Add TreeHeight task solution

Author: andrei-punko

Diff for: src/main/java/by/andd3dfx/tree/TreeHeight.java

@@ -0,0 +1,30 @@
+package by.andd3dfx.tree;
+
+import lombok.AllArgsConstructor;
+
+/**
+ * Determine height/depth of binary tree
+ */
+public class TreeHeight {
+
+    public static int calcHeight(Node node) {
+        if (node == null) {
+            return 0;
+        }
+
+        var leftHeight = calcHeight(node.left);
+        var rightHeight = calcHeight(node.right);
+        return 1 + Math.max(leftHeight, rightHeight);
+    }
+
+    @AllArgsConstructor
+    public static class Node {
+        int value;
+        Node left;
+        Node right;
+
+        public Node(int value) {
+            this.value = value;
+        }
+    }
+}

Diff for: src/test/java/by/andd3dfx/tree/TreeHeightTest.java

@@ -0,0 +1,21 @@
+package by.andd3dfx.tree;
+
+import by.andd3dfx.tree.TreeHeight.Node;
+import org.junit.Test;
+
+import static by.andd3dfx.tree.TreeHeight.calcHeight;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class TreeHeightTest {
+
+    @Test
+    public void testCalcHeight() {
+        var two = new Node(2);
+        var three = new Node(3, new Node(4), null);
+        Node root = new Node(1, two, three);
+
+        assertThat(calcHeight(root)).isEqualTo(3);
+        assertThat(calcHeight(two)).isEqualTo(1);
+        assertThat(calcHeight(three)).isEqualTo(2);
+    }
+}