From b1caccfe266c25cd9fdec359a9b4af0d8259f2b9 Mon Sep 17 00:00:00 2001
From: Ivaylo Ivanov <me@ivayloivanov.eu>
Date: Fri, 15 Oct 2021 19:30:29 +0200
Subject: [PATCH] Add UE1 A.2

---
 Dockerfile       |  4 ++++
 code/Aufgabe1.hs | 58 ++++++++++++++++++++++++++++++------------------
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/Dockerfile b/Dockerfile
index 6dd274a..5720b94 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,3 +1,7 @@
 FROM haskell:buster
 
 RUN apt-get update && apt-get install -y haskell-platform
+
+WORKDIR /opt
+
+CMD ["ghci"]
diff --git a/code/Aufgabe1.hs b/code/Aufgabe1.hs
index fd2314e..52b8407 100644
--- a/code/Aufgabe1.hs
+++ b/code/Aufgabe1.hs
@@ -16,9 +16,6 @@ type Zerlegungszeugen    = [Zerlegungszeuge]
 
 
 -- Aufgabe A.1
-
-ist_tzr :: Zeichenreihe -> Teilzeichenreihe -> IstTeilzeichenreihe
-
 {-
     Solution:
     - if both strings are the same, True
@@ -29,26 +26,49 @@ ist_tzr :: Zeichenreihe -> Teilzeichenreihe -> IstTeilzeichenreihe
       If it is not, the first string will get smaller than the second eventually and the function will return False
 -}
 
-ist_tzr x y
-    | y == x = True
-    | y == [] = True
-    | length y > length x = False
+ist_tzr :: Zeichenreihe -> Teilzeichenreihe -> IstTeilzeichenreihe
+
+ist_tzr z t
+    | t == z = True
+    | t == [] = True
+    | length t > length z = False
     | otherwise =
-        if head x == head y then
-            ist_tzr (tail x) (tail y)
+        if head z == head t then
+            ist_tzr (tail z) (tail t)
         else
-            ist_tzr (tail x) y
-
-
+            ist_tzr (tail z) t
 
 -- Aufgabe A.2
-
---tzr_zeuge :: Zeichenreihe -> Teilzeichenreihe -> Zerlegungszeuge
-
-{- Knapp, aber gut nachvollziehbar geht tzr_zeuge folgendermassen vor:
-   ...
+{-
+    Solution:
+    - the base cases are as follows:
+        - both strings are empty, return a triple with empty strings
+        - the second string is empty, return a triple with empty strings as first two elements and the whole first string as a third.
+          The problem description states that the split doesn't matter, so we take this because it is easy and cheap to do :)
+        - the second string is not a subset of the first string, return the "error triple"
+    - for handling the other cases:
+        - we find the position of the last subset string in the first string
+        - we take all of the characters until this position - this is the first element of the triple
+        - we then take all of the characters after this position summed with the length of the second string - this is the third element of the triple
 -}
 
+tzr_zeuge :: Zeichenreihe -> Teilzeichenreihe -> Zerlegungszeuge
+tzr_zeuge [] [] =  ("", "", "")
+tzr_zeuge z [] = ("", "", z)
+tzr_zeuge z t
+    | not (ist_tzr z t) = ("", t ++ t, "")
+    | otherwise =
+        let pos = (find_tzr_position z t 0) - 1
+            pre = take (pos) z
+            suf = drop (pos + (length t)) z
+        in (pre, t, suf)
+
+-- find the index of the last occurrence of t in z
+find_tzr_position :: Zeichenreihe -> Teilzeichenreihe -> Nat0 -> Nat0
+find_tzr_position (z:zs) t n
+    | not (ist_tzr (z:zs) t) = n
+    | otherwise = find_tzr_position zs t (n + 1)
+
 -- Aufgabe A.3
 
 --tzr_zeugen :: Zeichenreihe -> Teilzeichenreihe -> Zerlegungszeugen
@@ -65,7 +85,3 @@ ist_tzr x y
 {- Knapp, aber gut nachvollziehbar geht wieOft folgendermassen vor:
    ...
 -}
-
-
-
-