diff --git a/makefile b/makefile
index 5893c0b..fdb61da 100644
--- a/makefile
+++ b/makefile
@@ -38,6 +38,12 @@ $(program_obj_filesobj_files): %.o: %.c
 unitTests: stack.o test_stack.c $(unityfolder)/unity.c
 	$(CC) $(FLAGS) -I$(unityfolder) -o runStackTest test_stack.c stack.o $(unityfolder)/unity.c
 
+# --------------------------
+# numbers.c Tests
+# --------------------------
+numbersTests: numbers.o test_numbers.c $(unityfolder)/unity.c
+	$(CC) $(FLAGS) -I$(unityfolder) -o runNumbersTest test_numbers.c numbers.o $(unityfolder)/unity.c
+
 # --------------------------
 # Clean
 # --------------------------
diff --git a/numbers.c b/numbers.c
index f59d9a2..7adf6bd 100644
--- a/numbers.c
+++ b/numbers.c
@@ -5,22 +5,140 @@
 #include "numbers.h"
 #include "bintree.h"
 
-//TODO: getDuplicate und createNumbers implementieren
+// TODO: getDuplicate und createNumbers implementieren
 /*  *   * Erzeugen eines Arrays mit der vom Nutzer eingegebenen Anzahl an Zufallszahlen.
-  * Sicherstellen, dass beim Befüllen keine Duplikate entstehen.
-  * Duplizieren eines zufälligen Eintrags im Array.
-  * in `getDuplicate()`: Sortieren des Arrays und Erkennen der doppelten Zahl durch Vergleich benachbarter Elemente. */
+ * Sicherstellen, dass beim Befüllen keine Duplikate entstehen.
+ * Duplizieren eines zufälligen Eintrags im Array.
+ * in `getDuplicate()`: Sortieren des Arrays und Erkennen der doppelten Zahl durch Vergleich benachbarter Elemente. */
 
 // Returns len random numbers between 1 and 2x len in random order which are all different, except for two entries.
 // Returns NULL on errors. Use your implementation of the binary search tree to check for possible duplicates while
 // creating random numbers.
+unsigned int checkArray(unsigned int *array, unsigned int len, unsigned int number)
+{
+  int free = 1;
+
+  for (int i = 0; i < len; i++)
+  {
+    if (array[i] == number)
+    {
+      free = 0;
+    }
+  }
+
+  return free;
+}
+
 unsigned int *createNumbers(unsigned int len)
 {
+  srand(time(NULL));
+  unsigned int array[len];
+  unsigned int randomNr;
 
+  for (int i = 0; i < len; i++)
+  {
+    do
+    {
+      randomNr = rand() % 2 * len + 1;
+    } while (!checkArray(array, i, randomNr));
+
+    array[i] = randomNr;
+  }
+
+  return array;
+}
+
+void merge(unsigned int arr[], unsigned int left, unsigned int mid, unsigned int right)
+{
+  unsigned int i, j, k;
+  unsigned int n1 = mid - left + 1;
+  unsigned int n2 = right - mid;
+
+  // Create temporary arrays
+  unsigned int leftArr[n1], rightArr[n2];
+
+  // Copy data to temporary arrays
+  for (i = 0; i < n1; i++)
+    leftArr[i] = arr[left + i];
+  for (j = 0; j < n2; j++)
+    rightArr[j] = arr[mid + 1 + j];
+
+  // Merge the temporary arrays back into arr[left..right]
+  i = 0;
+  j = 0;
+  k = left;
+  while (i < n1 && j < n2)
+  {
+    if (leftArr[i] <= rightArr[j])
+    {
+      arr[k] = leftArr[i];
+      i++;
+    }
+    else
+    {
+      arr[k] = rightArr[j];
+      j++;
+    }
+    k++;
+  }
+
+  // Copy the remaining elements of leftArr[], if any
+  while (i < n1)
+  {
+    arr[k] = leftArr[i];
+    i++;
+    k++;
+  }
+
+  // Copy the remaining elements of rightArr[], if any
+  while (j < n2)
+  {
+    arr[k] = rightArr[j];
+    j++;
+    k++;
+  }
+}
+
+void mergeSort(unsigned int arr[], unsigned int left, unsigned int right)
+{
+  if (left < right)
+  {
+
+    // Calculate the midpoint
+    unsigned int mid = left + (right - left) / 2;
+
+    // Sort first and second halves
+    mergeSort(arr, left, mid);
+    mergeSort(arr, mid + 1, right);
+
+    // Merge the sorted halves
+    merge(arr, left, mid, right);
+  }
 }
 
 // Returns only the only number in numbers which is present twice. Returns zero on errors.
 unsigned int getDuplicate(const unsigned int numbers[], unsigned int len)
 {
+  unsigned int temp[len];
+  unsigned int duplicate = 0;
 
+  for (int i = 0; i < len; i++)
+  {
+    temp[i] = numbers[i];
+  }
+  
+  // Sorting arr using mergesort
+  mergeSort(temp, 0, len - 1);
+
+  for (int i = 0; i < len - 1; i++)
+  {
+    duplicate = temp[i];
+    if (duplicate == temp[i + 1])
+    {
+      
+      break;
+    }
+  }
+
+  return duplicate;
 }
\ No newline at end of file
diff --git a/numbers.o b/numbers.o
new file mode 100644
index 0000000..507642a
Binary files /dev/null and b/numbers.o differ
diff --git a/runNumbersTest.exe b/runNumbersTest.exe
new file mode 100644
index 0000000..e9feb27
Binary files /dev/null and b/runNumbersTest.exe differ
diff --git a/test_numbers.c b/test_numbers.c
new file mode 100644
index 0000000..ae339ad
--- /dev/null
+++ b/test_numbers.c
@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "numbers.h"
+#include "unity.h"
+
+void duplicateTest()
+{
+    unsigned int array[6] = {1, 4, 5, 2, 3, 1};
+    unsigned int len = 6;
+
+    TEST_ASSERT_EQUAL_INT(1, getDuplicate(array, len));
+}
+
+void setUp(void)
+{
+    // Falls notwendig, kann hier Vorbereitungsarbeit gemacht werden
+}
+
+void tearDown(void)
+{
+    // Hier kann Bereinigungsarbeit nach jedem Test durchgeführt werden
+}
+
+int main()
+{
+    UNITY_BEGIN();
+
+    printf("============================\nNumbers tests\n============================\n");
+
+    RUN_TEST(duplicateTest);
+
+    return UNITY_END();
+}
\ No newline at end of file