diff --git a/numbers.c b/numbers.c
index f59d9a2..8ba720f 100644
--- a/numbers.c
+++ b/numbers.c
@@ -14,13 +14,91 @@
 // 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.
+
+// Vergleichsfunktion für qsort
+static int cmp_uint(const void *a, const void *b)
+{
+    unsigned int x = *(const unsigned int*)a;
+    unsigned int y = *(const unsigned int*)b;
+
+    if (x < y) return -1;
+    if (x > y) return 1;
+    return 0;
+}
+
 unsigned int *createNumbers(unsigned int len)
 {
+    if (len < 2) {
+        return NULL;
+    }
 
+    unsigned int *arr = malloc(len * sizeof(unsigned int));
+    if (!arr) {
+        return NULL;
+    }
+
+    BinTree *tree = createTree();
+    if (!tree) {
+        free(arr);
+        return NULL;
+
+    /* Zahlen generieren: keine Duplikate */
+    for (unsigned int i = 0; i < len; i++) {
+
+        unsigned int value;
+        int inserted = 0;
+
+        while (!inserted) {
+            value = (rand() % (2 * len)) + 1;
+
+            if (!search(tree, value)) {
+                insert(tree, value);
+                inserted = 1;
+            }
+        }
+
+        arr[i] = value;
+    /* Ein zufälliges Element duplizieren */
+    unsigned int a = rand() % len;
+    unsigned int b;
+
+    do {
+        b = rand() % len;
+    } while (b == a);
+
+    arr[b] = arr[a];
+
+    freeTree(tree);
+    return arr;
+    }
+  }
 }
 
 // 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)
 {
+  if (!numbers || len < 2) {
+        return 0;
+    }
 
+    unsigned int *tmp = malloc(len * sizeof(unsigned int));
+    if (!tmp) {
+        return 0;
+    }
+
+    memcpy(tmp, numbers, len * sizeof(unsigned int));
+
+    qsort(tmp, len, sizeof(unsigned int), cmp_uint);
+
+    unsigned int duplicate = 0;
+
+    for (unsigned int i = 1; i < len; i++) {
+        if (tmp[i] == tmp[i - 1]) {
+            duplicate = tmp[i];
+            break;
+        }
+    }
+
+    free(tmp);
+    return duplicate;
 }
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