diff --git a/Double b/Double
new file mode 160000
index 0000000..92bb8b7
--- /dev/null
+++ b/Double
@@ -0,0 +1 @@
+Subproject commit 92bb8b73d30806f24e365607346c2fa96a54d850
diff --git a/bintree.c b/bintree.c
index 5cf82a9..638f8e5 100644
--- a/bintree.c
+++ b/bintree.c
@@ -1,3 +1,4 @@
+#include <stdlib.h>
 #include <string.h>
 #include "stack.h"
 #include "bintree.h"
@@ -12,7 +13,32 @@
 // if isDuplicate is NULL, otherwise ignores duplicates and sets isDuplicate to 1 (or to 0 if a new entry is added).
 TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize, CompareFctType compareFct, int *isDuplicate)
 {
+    if (root == NULL) {
+        TreeNode *node = (TreeNode *)malloc(sizeof(TreeNode));
+        if (node == NULL) return NULL;
+        node->data = malloc(dataSize);
+        if (node->data == NULL) { free(node); return NULL; }
+        memcpy(node->data, data, dataSize);
+        node->left = node->right = NULL;
+        if (isDuplicate) *isDuplicate = 0;
+        return node;
+    }
 
+    int cmp = compareFct(data, root->data);
+    if (cmp < 0) {
+        root->left = addToTree(root->left, data, dataSize, compareFct, isDuplicate);
+    } else if (cmp > 0) {
+        root->right = addToTree(root->right, data, dataSize, compareFct, isDuplicate);
+    } else { // cmp == 0 -> duplicate
+        if (isDuplicate) {
+            *isDuplicate = 1;
+            return root;
+        } else {
+            // accept duplicates when isDuplicate == NULL: insert to the right subtree
+            root->right = addToTree(root->right, data, dataSize, compareFct, NULL);
+        }
+    }
+    return root;
 }
 
 // Iterates over the tree given by root. Follows the usage of strtok. If tree is NULL, the next entry of the last tree given is returned in ordering direction.
@@ -20,17 +46,48 @@ TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize, CompareFc
 // push the top node and push all its left nodes.
 void *nextTreeData(TreeNode *root)
 {
+    static StackNode *iterStack = NULL;
 
+    if (root != NULL) {
+        // (re)initialize iterator for new tree
+        clearStack(iterStack);
+        iterStack = NULL;
+        TreeNode *cur = root;
+        while (cur != NULL) {
+            iterStack = push(iterStack, cur);
+            cur = cur->left;
+        }
+    }
+
+    if (iterStack == NULL) return NULL;
+
+    TreeNode *node = (TreeNode *)top(iterStack);
+    iterStack = pop(iterStack);
+    void *ret = node->data;
+
+    // push right subtree (and all its left descendants)
+    TreeNode *cur = node->right;
+    while (cur != NULL) {
+        iterStack = push(iterStack, cur);
+        cur = cur->left;
+    }
+
+    return ret;
 }
 
 // Releases all memory resources (including data copies).
 void clearTree(TreeNode *root)
 {
-
+    if (root == NULL) return;
+    clearTree(root->left);
+    clearTree(root->right);
+    free(root->data);
+    free(root);
 }
 
 // Returns the number of entries in the tree given by root.
 unsigned int treeSize(const TreeNode *root)
 {
-
+    if (root == NULL) return 0;
+    return 1 + treeSize(root->left) + treeSize(root->right);
 }
\ No newline at end of file
diff --git a/bintree.o b/bintree.o
new file mode 100644
index 0000000..5d9c075
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diff --git a/doble.exe b/doble.exe
new file mode 100644
index 0000000..6120469
Binary files /dev/null and b/doble.exe differ
diff --git a/highscore.o b/highscore.o
new file mode 100644
index 0000000..ffbf6b0
Binary files /dev/null and b/highscore.o differ
diff --git a/highscores.txt b/highscores.txt
index 4edd5a7..b89d2a8 100644
--- a/highscores.txt
+++ b/highscores.txt
@@ -1 +1,4 @@
+player_name;11898
+Test;9953
+player_name;9927
 player1;3999
diff --git a/main.o b/main.o
new file mode 100644
index 0000000..93deeec
Binary files /dev/null and b/main.o differ
diff --git a/numbers.c b/numbers.c
index f59d9a2..26c5c7d 100644
--- a/numbers.c
+++ b/numbers.c
@@ -5,22 +5,95 @@
 #include "numbers.h"
 #include "bintree.h"
 
-//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. */
+static int compareUnsigned(const void *a, const void *b)
+{
+    unsigned int va = *(const unsigned int *)a;
+    unsigned int vb = *(const unsigned int *)b;
+    if (va < vb) return -1;
+    if (va > vb) return 1;
+    return 0;
+}
 
 // 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 *createNumbers(unsigned int len)
 {
+    if (len < 2) return NULL;
 
+    unsigned int *arr = (unsigned int *)malloc(len * sizeof(unsigned int));
+    if (arr == NULL) return NULL;
+
+    TreeNode *root = NULL;
+    /* create len-1 unique values in range [1, 2*len] */
+    srand((unsigned int)time(NULL));
+
+    while (treeSize(root) < len - 1) {
+        unsigned int v = (unsigned int)(rand() % (2 * len)) + 1;
+        int isDup = 0;
+        TreeNode *newRoot = addToTree(root, &v, sizeof(unsigned int), compareUnsigned, &isDup);
+        if (newRoot == NULL && root != NULL) { // allocation failed
+            clearTree(root);
+            free(arr);
+            return NULL;
+        }
+        root = newRoot;
+        /* if duplicate, addToTree left tree unchanged; loop continues */
+    }
+
+    /* extract values from tree (in-order) into arr[0..len-2] */
+    unsigned int idx = 0;
+    void *data = nextTreeData(root); // initializes iterator
+    while (data != NULL && idx < len - 1) {
+        arr[idx++] = *(unsigned int *)data;
+        data = nextTreeData(NULL);
+    }
+
+    if (idx != len - 1) {
+        clearTree(root);
+        free(arr);
+        return NULL;
+    }
+
+    /* pick a random existing index and duplicate it */
+    unsigned int dupIndex = (unsigned int)(rand() % (len - 1));
+    arr[len - 1] = arr[dupIndex];
+
+    /* free tree memory */
+    clearTree(root);
+
+    /* shuffle array */
+    for (unsigned int i = len - 1; i > 0; --i) {
+        unsigned int j = (unsigned int)(rand() % (i + 1));
+        unsigned int tmp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = tmp;
+    }
+
+    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 == NULL || len < 2) return 0;
 
+    TreeNode *root = NULL;
+    for (unsigned int i = 0; i < len; ++i) {
+        unsigned int v = numbers[i];
+        int isDup = 0;
+        TreeNode *newRoot = addToTree(root, &v, sizeof(unsigned int), compareUnsigned, &isDup);
+        if (newRoot == NULL && root != NULL) { // allocation failed
+            clearTree(root);
+            return 0;
+        }
+        root = newRoot;
+        if (isDup) {
+            clearTree(root);
+            return v;
+        }
+    }
+
+    clearTree(root);
+    return 0;
 }
\ No newline at end of file
diff --git a/numbers.o b/numbers.o
new file mode 100644
index 0000000..fa6b51a
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diff --git a/stack.c b/stack.c
index e3a90d4..6970da5 100644
--- a/stack.c
+++ b/stack.c
@@ -1,33 +1,39 @@
 #include <stdlib.h>
 #include "stack.h"
 
-//TODO: grundlegende Stackfunktionen implementieren:
-/*  * `push`: legt ein Element oben auf den Stack,
-    * `pop`: entfernt das oberste Element,
-    * `top`: liefert das oberste Element zurück,
-    * `clearStack`: gibt den gesamten Speicher frei. */
-
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data)
 {
-
+    StackNode *node = (StackNode*)malloc(sizeof(StackNode));
+    if (node == NULL) return stack; // allocation failed, return unchanged stack
+    node->data = data;
+    node->next = stack;
+    return node;
 }
 
 // Deletes the top element of the stack (latest added element) and releases its memory. (Pointer to data has to be
 // freed by caller.)
 StackNode *pop(StackNode *stack)
 {
-
+    if (stack == NULL) return NULL;
+    StackNode *next = stack->next;
+    free(stack);
+    return next;
 }
 
 // Returns the data of the top element.
 void *top(StackNode *stack)
 {
-
+    return (stack != NULL) ? stack->data : NULL;
 }
 
 // Clears stack and releases all memory.
 void clearStack(StackNode *stack)
 {
-
+    while (stack != NULL)
+    {
+        StackNode *next = stack->next;
+        free(stack);
+        stack = next;
+    }
 }
\ No newline at end of file
diff --git a/stack.h b/stack.h
index f7d542d..8f8824b 100644
--- a/stack.h
+++ b/stack.h
@@ -8,6 +8,10 @@ The latest element is taken from the stack. */
 #include <stdlib.h>
 
 //TODO: passenden Datentyp als struct anlegen
+typedef struct StackNode {
+    void *data;
+    struct StackNode *next;
+} StackNode;
 
 // Pushes data as pointer onto the stack.
 StackNode *push(StackNode *stack, void *data);
diff --git a/stack.o b/stack.o
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index 0000000..a4b3089
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diff --git a/timer.o b/timer.o
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index 0000000..248a165
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