E20 Ex 12 + 13

Exercises/E20_Lists/Exercise_12.cs

@@ -25,8 +25,15 @@ namespace Exercises_C_Sharp.E20_Lists
         static List<string> Meth(List<string> lis, char c)
         {
             /*Code START*/
+            List<string> tempList = [];
 
-            return new List<string>();
+            foreach(var element in lis)
+                if(!element.Contains(c))
+                    tempList.Add(element);
+
+            return tempList;
+            //ODER:
+            return lis.Where(k => !k.Contains(c)).ToList();
             /*Code ENDE*/
         }
     }

Exercises/E20_Lists/Exercise_13.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.Collections.Generic;
+using Microsoft.VisualBasic;
 
 namespace Exercises_C_Sharp.E20_Lists
 {
@@ -20,9 +21,49 @@ namespace Exercises_C_Sharp.E20_Lists
         static List<int> Meth(List<int> lis)
         {
             /*Code START*/
+            var newList = MakeKehrwertList(lis);
+            newList.Sort();
+            newList = MakeKehrwertList(newList);
 
-            return new List<int>();
+            return newList;
+
+            //ODER:
+            lis.Sort((k, l) => MakeKehrwert(k).CompareTo(MakeKehrwert(l)));
+            return lis;
+            
             /*Code ENDE*/
         }
+        static List<int> MakeKehrwertList(List<int> list)
+        {
+            List<int> temp = [];
+            foreach(var element in list)
+                temp.Add(MakeKehrwert(element));
+            return temp;
+        }
+
+        static int MakeKehrwert(int i)
+        {
+            int res = 0;
+            i *= 10;
+
+            while(i / 10 != 0)
+            {
+                i /= 10;
+                res *= 10;
+                res += i % 10;
+            }
+
+            return res;
+        }
+        static int MakeKehrwertString(int i)
+        {
+            string newI = i.ToString();
+            string temp = "";
+
+            for(int k = newI.Length - 1; k >= 0; k--)
+                temp += newI[k];
+
+            return Convert.ToInt32(temp);
+        }
     }
 }