wrapping my head around this double pointer thing:

c/arraylist.c

@@ -1,24 +1,29 @@
+#include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 
-typedef struct ArrayList {
-    int capacity;
-    int index;
-    int data[];
-} ArrayList;
+typedef struct i32_ArrayList {
+    int     capacity;  // capacity of the array
+    int     index;     // the current location the list that is to be written to
+    int32_t data[];    // the data
+} i32_ArrayList;
+
+i32_ArrayList* new_arraylist(int cap) {
+    i32_ArrayList* arr = malloc(sizeof(i32_ArrayList) + cap * sizeof(int));
+
+    if (arr == NULL) {
+        printf("ERROR: there was an error attemping to allocate memory for i32_ArrayList\n");
+        exit(1);
+    }
 
-ArrayList* new_arraylist(int cap) {
-    ArrayList* arr = malloc(sizeof(ArrayList) + cap * sizeof(int));
     arr->capacity = cap;
     arr->index = 0;
-    for (int i = 0; i < cap; i++) {
-        arr->data[i] = 0;
-    }
 
     return arr;
 }
 
-void push_to_array(ArrayList* s, int v) {
+// add to end of the array
+void array_append(i32_ArrayList* s, int v) {
     if (s->index == s->capacity) {
         printf("you attempted to insert %d, but array is at capacity cannot add mode values\n", v);
     } else {
@@ -27,35 +32,141 @@ void push_to_array(ArrayList* s, int v) {
     }
 }
 
-void pop_from_array(ArrayList* s) {
+void resize_arraylist(i32_ArrayList** arr) {
+    int            new_size = (*arr)->capacity * 2;
+    i32_ArrayList* new_arr = realloc((*arr), (sizeof(int) * new_size) + sizeof(i32_ArrayList));
+
+    if (new_arr == NULL) {
+        fprintf(stderr, "ERROR: unable to resize array\n");
+        exit(1);
+    }
+
+    (*arr) = new_arr;
+    (*arr)->capacity = new_size;
+}
+
+void array_append2(i32_ArrayList* arr, int v) {
+    if (arr->index == arr->capacity) {
+        // lets just double the capacity
+        resize_arraylist(&arr);
+        printf("size of arr: %d\n", arr->capacity);
+    }
+
+    array_append(arr, v);
+}
+
+// create an array list and fill in with values from array
+i32_ArrayList* new_arraylist_from_array(int cap, int* arr) {
+    i32_ArrayList* out = new_arraylist(cap);
+    for (int i = 0; i < cap; i++) {
+        array_append(out, arr[i]);
+    }
+
+    return (out);
+}
+
+// insert value at index
+// the strategy here is to start from the last element in the array and shift it to the right
+// gotta be careful and check that the index + 1 <= capacity otherwise we are in trouble
+void array_insert_at(i32_ArrayList* arr, int at_index, int32_t value) {
+    if (at_index == arr->index) {
+        array_append(arr, value);
+    }
+
+    if (at_index + 1 > arr->capacity) {
+        printf("ERROR: this insert is not possible since the shift required would be over the capacity of the array\n");
+        printf("You requested insert at %d but array capacity is set to %d\n", at_index, arr->capacity);
+    }
+
+    for (int i = arr->index; i >= at_index; i--) {
+        arr->data[i + 1] = arr->data[i];
+    }
+    arr->data[at_index] = value;
+}
+
+int32_t array_get_at(i32_ArrayList* arr, int index) {
+    return (arr->data[index]);
+}
+
+int32_t pop_from_array(i32_ArrayList* s) {
     if (s->index == 0) {
         printf("there is nothing to remove!\n");
+        return (-99);
     } else {
+        int32_t val = s->data[s->index - 1];
         s->index--;
+
+        return (val);
     }
 }
 
-void grow_array_list(ArrayList* s, int amount) {
+void grow_array_list(i32_ArrayList* s, int amount) {
 }
 
-void print_array_list(ArrayList* arr) {
+void print_array_list(i32_ArrayList* arr) {
     printf("[");
     for (int i = 0; i < arr->index; i++) {
         printf(" %d ", arr->data[i]);
     }
-    printf("]\n");
+    printf("]\t<capacity: %d; index: %d>\n", arr->capacity, arr->index);
 }
 
 int main() {
-    ArrayList* a = new_arraylist(5);
-    push_to_array(a, 10);
-    push_to_array(a, 11);
-    push_to_array(a, 12);
-    push_to_array(a, 12);
-    push_to_array(a, 12);
-    push_to_array(a, 12);
-    push_to_array(a, 12);
-    pop_from_array(a);
-    push_to_array(a, 155);
+    i32_ArrayList* a = new_arraylist(5);
+    int            arr_values[5] = {1, 2, 3, 4, 5};
+    i32_ArrayList* b = new_arraylist_from_array(5, arr_values);
+    print_array_list(b);
+
+    // these should all work just fine
+    array_append(a, 10);
     print_array_list(a);
-}
+    array_append(a, 11);
+    print_array_list(a);
+    array_append(a, 12);
+    print_array_list(a);
+    array_append(a, 13);
+    print_array_list(a);
+    array_append(a, 14);
+    print_array_list(a);
+
+    // this one will error
+    array_append(a, 100);
+
+    // so we remove one and then add
+    pop_from_array(a);
+    print_array_list(a);
+    array_append(a, 100);
+    print_array_list(a);
+
+    // now we test inserting different index
+    array_insert_at(a, 3, 55);
+    print_array_list(a);
+    array_insert_at(a, 4, 555);
+    print_array_list(a);
+
+    // what happens if try to insert at the last element
+    // this first implementation of the araylist will just overwrite this value
+    array_insert_at(a, 4, 100);
+    print_array_list(a);
+
+    // what if insert at 3 in this first version?
+    // this will shift the current 3 to 4, but this causes the 100 to be removed
+    array_insert_at(a, 3, 123);
+    print_array_list(a);
+
+    // lets implement v2 versions of these function that will grow
+    // the array when required
+    array_append2(a, 5656);
+    print_array_list(a);
+
+    // array_append(a, 14);
+    // print_array_list(a);
+    // pop_from_array(a);
+    // print_array_list(a);
+    // array_insert_at(a, 5, 90000);
+    // print_array_list(a);
+    // array_insert_at(a, 3, 1000);
+    // array_insert_at(a, 4, 1000);
+    // array_insert_at(a, 5, 10001);
+    // print_array_list(a);
+}

c/binary-tree.c

@@ -167,6 +167,22 @@ void print_stack(Stack* stack) {
     }
 }
 
+void print_stack_v2(Stack* stack) {
+    if (stack->len == 0) {
+        printf("ERROR: empty stack\n");
+    } else {
+        printf("[ ");
+        int   counter = 0;
+        Node* curr = stack->head;
+        while (counter < stack->len) {
+            printf("%d ", curr->value);
+            curr = curr->prev;
+            counter++;
+        }
+        printf(" ]\n");
+    }
+}
+
 int main() {
     /* lets create the following tree
                 12
@@ -192,10 +208,12 @@ int main() {
     walk_tree_post_order(root_node, post_stack);
     walk_tree_in_order(root_node, in_order_stack);
 
-    printf("the len of the stack is %d\n", stack->len);
-    print_stack(stack);
-    print_stack(post_stack);
-    print_stack(in_order_stack);
+    printf("pre order:  ", stack->len);
+    print_stack_v2(stack);
+    printf("in order:   ", stack->len);
+    print_stack_v2(post_stack);
+    printf("post order: ", stack->len);
+    print_stack_v2(in_order_stack);
     free(stack);
     free(post_stack);
     free(in_order_stack);

c/breadth-first-search.c

@@ -0,0 +1,202 @@
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct TreeNode {
+    int              value;
+    struct TreeNode* left;
+    struct TreeNode* right;
+} TreeNode;
+
+typedef struct Tree {
+    TreeNode* root;
+} Tree;
+
+/*  Set up data structures to be able to support the breadth first search of a tree */
+typedef struct QNode {
+    TreeNode*     tnode;  // this is the value of the QNode
+    struct QNode* next;
+} QNode;
+
+typedef struct Q {
+    QNode* head;
+    QNode* tail;
+    int    length;
+} Q;
+
+TreeNode* new_tree_node(int value) {
+    TreeNode* node = malloc(sizeof(TreeNode));
+    node->left = NULL;
+    node->right = NULL;
+    node->value = value;
+
+    return (node);
+}
+
+QNode* new_qnode(TreeNode* tnode) {
+    QNode* node = malloc(sizeof(QNode));
+    node->next = NULL;
+    node->tnode = tnode;
+
+    return (node);
+}
+
+Tree* new_tree(TreeNode* root) {
+    Tree* tree = malloc(sizeof(Tree));
+    tree->root = root;
+    return (tree);
+}
+
+Q* new_Q() {
+    Q* q = malloc(sizeof(Q));
+    q->head = NULL;
+    q->tail = NULL;
+    q->length = 0;
+
+    return (q);
+}
+
+void add_child_left(TreeNode* parent, TreeNode* node) {
+    if (parent->left != NULL) {
+        printf("ERROR: left child is non-empty\n");
+        exit(1);
+    } else {
+        parent->left = node;
+    }
+}
+
+void add_child_right(TreeNode* parent, TreeNode* node) {
+    if (parent->right != NULL) {
+        printf("ERROR: right child is non-empty\n");
+        exit(1);
+    } else {
+        parent->right = node;
+    }
+}
+
+// always add at tail
+void q_add_node(Q* q, QNode* node) {
+    if (q->length == 0) {
+        q->head = node;
+        q->tail = node;
+        q->length++;
+    } else {
+        q->tail->next = node;
+        q->tail = node;
+        q->length++;
+    }
+}
+
+// always remove from head
+TreeNode* q_remove_node(Q* q) {
+    QNode*    n = q->head;
+    TreeNode* tnode_at_head = n->tnode;
+    q->head = n->next;
+    q->length--;
+    free(n);
+    return (tnode_at_head);
+}
+
+/*
+
+[10, 5, 7, 12, 8, 88, 14]
+
+                10
+            5        7
+        12    8    88    14
+
+ */
+
+bool bf_search(Tree tree, int value) {
+    // start by adding th eroot of tree to the q
+    Q*     search_path = new_Q();
+    QNode* n = new_qnode(tree.root);
+    q_add_node(search_path, n);
+    TreeNode* current_value;
+    int       count_iterations = 1;
+    while (search_path->length > 0) {
+        count_iterations++;
+        current_value = q_remove_node(search_path);
+
+        if (current_value->value == value) {
+            free(search_path);
+            printf("total itarations: %d\n", count_iterations);
+            return (true);
+        }
+
+        if (current_value->left != NULL) {
+            q_add_node(search_path, new_qnode(current_value->left));
+        }
+        if (current_value->right != NULL) {
+            q_add_node(search_path, new_qnode(current_value->right));
+        }
+    }
+    printf("total itarations: %d\n", count_iterations);
+    free(search_path);
+    return (false);
+}
+
+bool is_leaf(TreeNode* a) {
+    if (a->left == NULL && a->right == NULL) {
+        return (true);
+    } else {
+        return (false);
+    }
+}
+
+// determine if two trees are equal
+bool tree_equal(TreeNode* root_a, TreeNode* root_b) {
+    if (root_a->value != root_b->value) {
+        return (false);
+    }
+
+    if (is_leaf(root_a) && is_leaf(root_b)) {
+        return (true);
+    }
+
+    if (is_leaf(root_a) || is_leaf(root_b)) {
+        return (false);
+    }
+
+    return (tree_equal(root_a->left, root_b->left) && tree_equal(root_a->right, root_b->right));
+}
+
+/*
+The reason for choose the Q as the data strucuture to keep track
+of the search path is to
+ */
+int main() {
+    TreeNode* root = new_tree_node(10);
+    TreeNode* root2 = new_tree_node(10);
+    Tree*     tree = new_tree(root);
+    Tree*     tree2 = new_tree(root2);
+
+    add_child_left(root, new_tree_node(5));
+    add_child_right(root, new_tree_node(7));
+
+    add_child_left(root->left, new_tree_node(12));
+    add_child_right(root->left, new_tree_node(8));
+
+    add_child_left(root->right, new_tree_node(88));
+    add_child_right(root->right, new_tree_node(14));
+
+    // create the second tree
+    add_child_left(root2, new_tree_node(5));
+    add_child_right(root2, new_tree_node(7));
+
+    add_child_left(root2->left, new_tree_node(12));
+    add_child_right(root2->left, new_tree_node(8));
+
+    add_child_left(root2->right, new_tree_node(88));
+    add_child_right(root2->right, new_tree_node(14));
+
+    bool answer;
+    answer = bf_search(*tree, 10);
+    printf("the answer is %s\n", answer ? "true" : "false");
+
+    bool trees_are_equal;
+    trees_are_equal = tree_equal(tree->root, tree2->root);
+    printf("are the trees equal? %s\n", trees_are_equal ? "yes" : "no");
+
+    return (0);
+}