diff --git a/src/main/kotlin/it/norangeb/algorithms/datastructures/dictionary/RedBlackBST.kt b/src/main/kotlin/it/norangeb/algorithms/datastructures/dictionary/RedBlackBST.kt
new file mode 100644
index 0000000..64ebf7a
--- /dev/null
+++ b/src/main/kotlin/it/norangeb/algorithms/datastructures/dictionary/RedBlackBST.kt
@@ -0,0 +1,90 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 norangebit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+package it.norangeb.algorithms.datastructures.dictionary
+
+import arrow.core.Option
+
+class RedBlackBST<K : Comparable<K>, V> : OrderedDictionary<K, V> {
+    override fun get(key: K): Option<V> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun set(key: K, value: V) {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun delete(key: K) {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun contains(key: K): Boolean {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun isEmpty(): Boolean {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun size(): Int {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun max(): Option<K> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun min(): Option<K> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun floor(key: K): Option<K> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun ceiling(key: K): Option<K> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun select(pos: Int): Option<K> {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun rank(key: K): Int {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun <R> preOrder(transform: (K) -> R) {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun <R> inOrder(transform: (K) -> R) {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+
+    override fun <R> postOrder(transform: (K) -> R) {
+        TODO("not implemented") // To change body of created functions use File | Settings | File Templates.
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/it/norangeb/algorithms/exam/Inbalance.kt b/src/main/kotlin/it/norangeb/algorithms/exam/Inbalance.kt
new file mode 100644
index 0000000..e18ca9f
--- /dev/null
+++ b/src/main/kotlin/it/norangeb/algorithms/exam/Inbalance.kt
@@ -0,0 +1,98 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 norangebit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+package it.norangeb.algorithms.exam
+
+import arrow.core.None
+import arrow.core.Option
+import arrow.core.toOption
+import kotlin.math.abs
+
+class Inbalance<K : Comparable<K>, V> {
+
+    private var root: Option<Node<K, V>> = None
+
+    operator fun set(key: K, value: V) {
+        root = set(key, value, root)
+    }
+
+    private fun set(
+        key: K,
+        value: V,
+        node: Option<Node<K, V>>
+    ): Option<Node<K, V>> = node.fold(
+        { Node(key, value) },
+        {
+            when {
+                key == it.key -> it.clone(value = value)
+                key > it.key -> it.clone(right = set(key, value, it.right))
+                else -> it.clone(left = set(key, value, it.left))
+            }
+        }).toOption()
+
+    operator fun get(key: K): Option<V> = get(key, root).map { it.value }
+
+    private fun get(
+        key: K,
+        node: Option<Node<K, V>>
+    ): Option<Node<K, V>> = node.flatMap {
+        when {
+            key == it.key -> node
+            key > it.key -> get(key, it.right)
+            else -> get(key, it.left)
+        }
+    }
+
+    fun inbalance(key: K): Option<Int> = get(key, root)
+        .map { computeInbalance(it) }
+
+    private fun computeInbalance(node: Node<K, V>): Int {
+        val leftLeaf = node.left.fold({ 0 }, { leaf(it) })
+        val rightLeaf = node.right.fold({ 0 }, { leaf(it) })
+
+        return abs(leftLeaf - rightLeaf)
+    }
+
+    private fun leaf(node: Node<K, V>): Int = when {
+        node.left == None && node.right == None -> 1
+        else ->
+            node.left.fold({ 0 }, { leaf(it) }) +
+                    node.right.fold({ 0 }, { leaf(it) })
+    }
+
+    private data class Node<K, V>(
+        val key: K,
+        val value: V,
+        val left: Option<Node<K, V>> = None,
+        val right: Option<Node<K, V>> = None
+    ) {
+        fun clone(
+            key: K = this.key,
+            value: V = this.value,
+            left: Option<Node<K, V>> = this.left,
+            right: Option<Node<K, V>> = this.right
+        ) = Node(key, value, left, right)
+    }
+}
\ No newline at end of file
diff --git a/src/test/kotlin/it/norangeb/algorithms/exam/InbalanceTest.kt b/src/test/kotlin/it/norangeb/algorithms/exam/InbalanceTest.kt
new file mode 100644
index 0000000..e7764e8
--- /dev/null
+++ b/src/test/kotlin/it/norangeb/algorithms/exam/InbalanceTest.kt
@@ -0,0 +1,125 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2019 norangebit
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ */
+
+package it.norangeb.algorithms.exam
+
+import arrow.core.None
+import arrow.core.Option
+import arrow.core.Some
+import org.amshove.kluent.`should equal`
+import org.spekframework.spek2.Spek
+import org.spekframework.spek2.style.gherkin.Feature
+
+object InbalanceTest : Spek({
+    Feature("inbalance") {
+        Scenario("get and set") {
+            val tree by memoized { Inbalance<Int, Int>() }
+
+            When("add couple 15-15, 13-13, 23-23, 5-5") {
+                tree[15] = 15
+                tree[13] = 13
+                tree[23] = 24
+                tree[5] = 5
+            }
+
+            Then("tree of 23 should equal 24") {
+                tree[23] `should equal` Some(24)
+            }
+
+            Then("tree of 25 should equal None") {
+                tree[25] `should equal` None
+            }
+
+            Then("tree of 5 should equal 5") {
+                tree[5] `should equal` Some(5)
+            }
+
+            When("add couple 1-1, 17-17, 25-25, 23-23") {
+                tree[1] = 1
+                tree[17] = 17
+                tree[25] = 25
+                tree[23] = 23
+            }
+
+            Then("tree of 23 should equal 23") {
+                tree[23] `should equal` Some(23)
+            }
+
+            Then("tree of 25 should equal 25") {
+                tree[25] `should equal` Some(25)
+            }
+        }
+
+        Scenario("inbalance") {
+            val tree by memoized { Inbalance<Int, Int>() }
+
+            Given("tree 15, 23, 7, 18, 25, 21, 22, 20") {
+                tree[15] = 15
+                tree[23] = 23
+                tree[7] = 7
+                tree[18] = 18
+                tree[25] = 25
+                tree[21] = 21
+                tree[22] = 22
+                tree[20] = 20
+                tree[10] = 10
+            }
+
+            lateinit var inbalance: Option<Int>
+
+            When("compute imbalance of 1") {
+                inbalance = tree.inbalance(1)
+            }
+
+            Then("inbalance should equal None") {
+                inbalance `should equal` None
+            }
+
+            When("compute imbalance of 23") {
+                inbalance = tree.inbalance(23)
+            }
+
+            Then("inbalance should equal 1") {
+                inbalance `should equal` Some(1)
+            }
+
+            When("compute inbalance of 15") {
+                inbalance = tree.inbalance(15)
+            }
+
+            Then("inbalance should equal 2") {
+                inbalance `should equal` Some(2)
+            }
+
+            When("compute inbalance of 10") {
+                inbalance = tree.inbalance(10)
+            }
+
+            Then("inbalance should equal 0") {
+                inbalance `should equal` Some(0)
+            }
+        }
+    }
+})
\ No newline at end of file