From 022c591d1ff008041f712e65149670f568404c1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=A9my=20Zurcher?= <jeremy@asynk.ch>
Date: Sun, 14 Apr 2013 18:12:34 +0200
Subject: Scala : objsets: implements TweetSet

---
 .../objsets/src/main/scala/objsets/TweetSet.scala  | 39 ++++++++++++++++++----
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/Scala/objsets/src/main/scala/objsets/TweetSet.scala b/Scala/objsets/src/main/scala/objsets/TweetSet.scala
index 9200c50..f558e48 100644
--- a/Scala/objsets/src/main/scala/objsets/TweetSet.scala
+++ b/Scala/objsets/src/main/scala/objsets/TweetSet.scala
@@ -42,7 +42,7 @@ abstract class TweetSet {
    * Question: Can we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-  def filter(p: Tweet => Boolean): TweetSet = ???
+  def filter(p: Tweet => Boolean): TweetSet = filterAcc(p, new Empty)
 
   /**
    * This is a helper method for `filter` that propagetes the accumulated tweets.
@@ -55,7 +55,7 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-   def union(that: TweetSet): TweetSet = ???
+   def union(that: TweetSet): TweetSet
 
   /**
    * Returns the tweet from this set which has the greatest retweet count.
@@ -66,7 +66,12 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-  def mostRetweeted: Tweet = ???
+  def mostRetweeted: Tweet
+
+  /**
+   * This is a helper method for `mostRetweeted` search the set transporting the challenger
+   */
+  def mostRetweetedElect(tweet: Tweet): Tweet
 
   /**
    * Returns a list containing all tweets of this set, sorted by retweet count
@@ -77,7 +82,7 @@ abstract class TweetSet {
    * Question: Should we implment this method here, or should it remain abstract
    * and be implemented in the subclasses?
    */
-  def descendingByRetweet: TweetList = ???
+  def descendingByRetweet: TweetList
 
 
   /**
@@ -110,7 +115,15 @@ abstract class TweetSet {
 
 class Empty extends TweetSet {
 
-  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = ???
+  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = acc
+
+  def union(that: TweetSet): TweetSet = that
+
+  def mostRetweeted: Tweet = throw new NoSuchElementException
+
+  def mostRetweetedElect(challenger: Tweet): Tweet = challenger
+
+  def descendingByRetweet: TweetList = Nil
 
 
   /**
@@ -128,7 +141,21 @@ class Empty extends TweetSet {
 
 class NonEmpty(elem: Tweet, left: TweetSet, right: TweetSet) extends TweetSet {
 
-  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet = ???
+  def filterAcc(p: Tweet => Boolean, acc: TweetSet): TweetSet =
+    if (p(elem)) right filterAcc(p, (left filterAcc(p, acc) incl elem))
+    else right filterAcc(p, left filterAcc(p, acc))
+
+  def union(that: TweetSet): TweetSet = (right union (left union that)) incl elem
+
+  def mostRetweeted: Tweet = mostRetweetedElect(elem)
+
+  def mostRetweetedElect(challenger: Tweet): Tweet =
+    right mostRetweetedElect (left mostRetweetedElect (if (elem.retweets > challenger.retweets) elem else challenger))
+
+  def descendingByRetweet: TweetList = {
+    val most = mostRetweetedElect(elem)
+    new Cons(most, remove(most).descendingByRetweet)
+  }
 
 
   /**
-- 
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