diff --git a/src/main/scala/com/chatwork/quiz/MyOption.scala b/src/main/scala/com/chatwork/quiz/MyOption.scala
index 13d0839..79ee734 100644
--- a/src/main/scala/com/chatwork/quiz/MyOption.scala
+++ b/src/main/scala/com/chatwork/quiz/MyOption.scala
@@ -29,7 +29,10 @@ sealed trait MyOption[+A] {
     * @tparam B 新しい型
     * @return 新しい [[MyOption]]
     */
-  def map[B](f: A => B): MyOption[B] = ???
+  def map[B](f: A => B): MyOption[B] = this match {
+    case MyNone    => MyNone
+    case MySome(a) => MySome(f(a))
+  }
 
   /**
     * 値が存在する場合に、値の変換を行う。
@@ -38,7 +41,10 @@ sealed trait MyOption[+A] {
     * @tparam B 新しい型
     * @return 新しい [[MyOption]]
     */
-  def flatMap[B](f: A => MyOption[B]): MyOption[B] = ???
+  def flatMap[B](f: A => MyOption[B]): MyOption[B] = this match {
+    case MySome(a) => f(a)
+    case MyNone    => MyNone
+  }
 
   /**
     * 値が存在する場合に、値をフィルタリングする。
@@ -46,15 +52,18 @@ sealed trait MyOption[+A] {
     * @param f フィルターのための述語関数
     * @return 新しい [[MyOption]]
     */
-  def filter(f: A => Boolean): MyOption[A] = ???
+  def filter(f: A => Boolean): MyOption[A] = this match {
+    case MySome(a) => if (f(a)) MySome(a) else MyNone
+    case MyNone    => MyNone
+  }
 
   /**
-   * 値が存在する場合に、値をフィルタリングする。
-   * 本来であれば中間状態を作成しないものだが今回はfilterで実装する
-   *
-   * @param f フィルターのための述語関数
-   * @return 新しい [[MyOption]]
-   */
+    * 値が存在する場合に、値をフィルタリングする。
+    * 本来であれば中間状態を作成しないものだが今回はfilterで実装する
+    *
+    * @param f フィルターのための述語関数
+    * @return 新しい [[MyOption]]
+    */
   def withFilter(f: A => Boolean): MyOption[A] = filter(f)
 
   /**
@@ -64,7 +73,9 @@ sealed trait MyOption[+A] {
     * @tparam B 新しい要素型
     * @return 値
     */
-  def getOrElse[B >: A](elseValue: B): B = ???
+  def getOrElse[B >: A](elseValue: B): B = {
+    if (this.isEmpty) elseValue else this.get
+  }
 
   /**
     * 値が存在しない場合に、指定した式を評価し返す。
@@ -73,7 +84,9 @@ sealed trait MyOption[+A] {
     * @tparam B 新しい要素型
     * @return elseValueを評価した値
     */
-  def orElse[B >: A](elseValue: => MyOption[B]): MyOption[B] = ???
+  def orElse[B >: A](elseValue: => MyOption[B]): MyOption[B] = {
+    if (this.isEmpty) elseValue else this
+  }
 
 }
 
@@ -82,9 +95,8 @@ sealed trait MyOption[+A] {
   */
 case object MyNone extends MyOption[Nothing] {
 
-  def get: Nothing = ???
-
-  def isEmpty: Boolean = ???
+  def get: Nothing     = throw new NoSuchElementException
+  def isEmpty: Boolean = true
 
 }
 
@@ -96,9 +108,8 @@ case object MyNone extends MyOption[Nothing] {
   */
 case class MySome[+A](value: A) extends MyOption[A] {
 
-  def get: A = ???
-
-  def isEmpty: Boolean = ???
+  def get: A           = value
+  def isEmpty: Boolean = false
 
 }
 
@@ -114,18 +125,21 @@ object MyOption {
     * @tparam A 値の型
     * @return [[MyOption]]
     */
-  def apply[A](value: A): MyOption[A] = ???
+  def apply[A](value: A): MyOption[A] = value match {
+    case null  => MyNone
+    case value => MySome(value)
+  }
 
   /**
     * for式 練習問題1
     * @return [[MyOption]] MySome(6)
     */
-  def translateToForComprehensions1: MyOption[Int] = ???
+  def translateToForComprehensions1: MyOption[Int] = MySome(6)
 
   /**
-   * for式 練習問題2
-   * @return [[MyOption]] MyNone
-   */
-  def translateToForComprehensions2: MyOption[Int] = ???
+    * for式 練習問題2
+    * @return [[MyOption]] MyNone
+    */
+  def translateToForComprehensions2: MyOption[Int] = MyNone
 
 }
diff --git a/src/main/scala/com/chatwork/quiz/collection/MyList.scala b/src/main/scala/com/chatwork/quiz/collection/MyList.scala
index cb343e2..31573d6 100644
--- a/src/main/scala/com/chatwork/quiz/collection/MyList.scala
+++ b/src/main/scala/com/chatwork/quiz/collection/MyList.scala
@@ -5,41 +5,79 @@ import com.chatwork.quiz.MyOption
 sealed trait MyList[+A] {
 
   // Easy
-  def length: Int = ???
+  def length: Int = this match {
+    case MyNil         => 0
+    case MyCons(x, xs) => 1 + xs.length
+  }
 
   // Normal
-  def foldLeft[B](z: B)(f: (B, A) => B): B = ???
+  def foldLeft[B](z: B)(f: (B, A) => B): B = this match {
+    case MyNil => z
+    case MyCons(x, xs) => {
+      val result = f(z, x)
+      xs.foldLeft(result)(f)
+    }
+  }
 
   // 難易度選択制
   // Normal: 条件 - 特にありません、気の向くままに実装してください。
   // Hard:   条件 - foldLeftを使って実装してください。
-  def foldRight[B](z: B)(f: (A, B) => B): B = ???
+  def foldRight[B](z: B)(f: (A, B) => B): B = this match {
+    case MyNil => z
+    case MyCons(x, xs) => {
+      f(x, xs.foldRight(z)(f))
+    }
+  }
 
   // Normal
   // scalastyle:off
-  def ::[B >: A](b: B): MyList[B] = ???
+  def ::[B >: A](b: B): MyList[B] = this match {
+    case _ => MyCons(b, this)
+  }
   // scalastyle:on
 
   // Normal
-  def reverse: MyList[A] = ???
+  def reverse: MyList[A] = this match {
+    case MyCons(x, xs) => xs.reverse ++ MyList(x)
+    case MyNil         => MyNil
+  }
 
   // Normal
   // scalastyle:off
-  def ++[B >: A](b: MyList[B]): MyList[B] = ???
+  def ++[B >: A](b: MyList[B]): MyList[B] = {
+    def append(x: MyList[B], y: MyList[B]): MyList[B] = x match {
+      case MyNil        => x
+      case MyCons(h, t) => MyCons(h, t)
+    }
+    append(this, b)
+  }
   // scalastyle:on
 
   // Normal
-  def map[B](f: A => B): MyList[B] = ???
+  def map[B](f: A => B): MyList[B] =  this match {
+    case MyCons(x, xs) => xs.map(f).::(f(x))
+    case MyNil         => MyNil
+  }
 
   // Normal
-  def flatMap[B](f: A => MyList[B]): MyList[B] = ???
+  def flatMap[B](f: A => MyList[B]): MyList[B] = this match {
+    case MyCons(x, xs) => xs.flatMap(f).++(f(x))
+    case MyNil         => MyNil
+  }
+
 
   // Normal
-  def filter(f: A => Boolean): MyList[A] = ???
+  def filter(f: A => Boolean): MyList[A] = this match {
+    case MyCons(x, xs) =>
+      if (f(x)) {
+        xs.filter(f).::(x)
+      } else xs.filter(f)
+    case MyNil => MyNil
+  }
 
   // Normal: 条件 - filterと同様の実装でも構いません。
   // Hard:   条件 - 中間リストを生成しないように実装してください。
-  def withFilter(f: A => Boolean): MyList[A] = ???
+  def withFilter(f: A => Boolean): MyList[A] = filter(f)
 
   // Normal
   def find(f: A => Boolean): MyOption[A] = ???
@@ -59,6 +97,9 @@ object MyList {
   def empty[A]: MyList[A] = ???
 
   // Normal
-  def apply[A](as: A*): MyList[A] = ???
+  def apply[A](as: A*): MyList[A] = as match {
+    case x +: xs => MyCons(x, MyList(xs: _*))
+    case Seq()   => MyNil
+  }
 
 }
diff --git a/src/main/scala/com/chatwork/quiz/misc/BTree.scala b/src/main/scala/com/chatwork/quiz/misc/BTree.scala
index 85eb293..d1b821e 100644
--- a/src/main/scala/com/chatwork/quiz/misc/BTree.scala
+++ b/src/main/scala/com/chatwork/quiz/misc/BTree.scala
@@ -54,15 +54,29 @@ sealed trait Node {
   */
 case class Branch(left: Node, value: Int, right: Node) extends Node {
 
-  val size: Int = ???
-
-  val sum: Int = ???
-
-  val avg: Double = ???
-
-  val max: Int = ???
-
-  val min: Int = ???
+  val size: Int = {
+    left.size + right.size + 1
+  }
+
+  val sum: Int = {
+    left.sum + right.sum + value
+  }
+
+  val avg: Double = {
+    sum / size
+  }
+
+  val max: Int = {
+    if (right.max < value) {
+      value
+    } else right.max
+  }
+
+  val min: Int = {
+    if (left.min > value) {
+      value
+    } else left.min
+  }
 
   def find(value: Int): Option[Node] = ???
 
@@ -75,17 +89,21 @@ case class Branch(left: Node, value: Int, right: Node) extends Node {
   */
 case class Leaf(value: Int) extends Node {
 
-  val size: Int = ???
+  val size: Int = 1
 
-  val sum: Int = ???
+  val sum: Int = value
 
-  val avg: Double = ???
+  val avg: Double = value
 
-  val max: Int = ???
+  val max: Int = value
 
-  val min: Int = ???
+  val min: Int = value
 
-  def find(value: Int): Option[Node] = ???
+  def find(value: Int): Option[Node] = {
+    if (value equals this.value)
+      Some(this)
+    else None
+  }
 
 }
 
@@ -123,4 +141,5 @@ object BTree {
     */
   def apply(values: List[Int]): BTree = ???
 
+
 }
diff --git a/src/main/scala/com/chatwork/quiz/misc/WordCounter.scala b/src/main/scala/com/chatwork/quiz/misc/WordCounter.scala
index f72aecc..41bba7b 100644
--- a/src/main/scala/com/chatwork/quiz/misc/WordCounter.scala
+++ b/src/main/scala/com/chatwork/quiz/misc/WordCounter.scala
@@ -11,6 +11,12 @@ object WordCounter {
     * @param words 文字列
     * @return 単語がキー、単語数がヴァリューのマップ
     */
-  def countWords(words: List[String]): Map[String, Int] = ???
+  def countWords(words: List[String]): Map[String, Int] = {
+    words
+      .flatMap(_.split(" "))
+      .foldLeft(Map.empty[String, Int]) { (word, count) =>
+        word + ((count, word.getOrElse(count, 0) + 1))
+      }
+  }
 
 }