diff --git a/lib/hash_map.c b/lib/hash_map.c
index 3ba70d1..a497925 100644
--- a/lib/hash_map.c
+++ b/lib/hash_map.c
@@ -123,7 +123,7 @@ struct hash_map *hash_map_initialization() {
   return hash_map;
 }
 
-void hash_map_add(struct hash_map *hash_map, string_t key, void *data) {
+void hash_map_add(struct hash_map *hash_map, string_t key_value, void *data) {
   if (hash_map->length == hash_map->capacity) {
     size_t previous_capacity = hash_map->capacity;
     hash_map->capacity += HASH_MAP_INITIAL_CAPACITY;
@@ -132,6 +132,7 @@ void hash_map_add(struct hash_map *hash_map, string_t key, void *data) {
       hash_map->items[index] = NULL;
     }
   }
+  string_t key = string_copy(key_value);
   uint64_t hash_value = hash(key, hash_map->capacity);
   struct linked_list *list = hash_map->items[hash_value];
   struct hash_map_item *item = malloc(sizeof(struct hash_map_item));
@@ -156,6 +157,9 @@ void hash_map_add(struct hash_map *hash_map, string_t key, void *data) {
     if (!found) {
       linked_list_add_in_head(list, (void *)item);
       hash_map->length++;
+    } else {
+      free(key);
+      free(item);
     }
   }
 }
@@ -172,10 +176,13 @@ void hash_map_remove(struct hash_map *hash_map, string_t key) {
     struct hash_map_item *item = (struct hash_map_item *)node->data;
     if (!string_equals(key, item->key)) {
       linked_list_add_in_head(new_list, item);
+    } else {
+      free(item->key);
+      free(item);
     }
     node = node->next;
   }
-  free(list);
+  linked_list_free(list);
   hash_map->items[hash_value] = new_list;
   hash_map->length--;
 }
@@ -220,10 +227,18 @@ string_t *hash_map_get_keys(struct hash_map *hash_map) {
 
 void hash_map_free(struct hash_map *hash_map) {
   for (size_t index = 0; index < hash_map->capacity; index++) {
-    if (hash_map->items[index] != NULL) {
-      free(hash_map->items[index]->head->data);
-      linked_list_free(hash_map->items[index]);
+    struct linked_list *list = hash_map->items[index];
+    if (list != NULL) {
+      struct linked_list_node *node = list->head;
+      while (node != NULL) {
+        struct hash_map_item *item = (struct hash_map_item *)node->data;
+        free(item->key);
+        free(item);
+        node = node->next;
+      }
+      linked_list_free(list);
     }
   }
+  free(hash_map->items);
   free(hash_map);
 }
diff --git a/lib/string.c b/lib/string.c
index 2876405..3d7ff45 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -87,8 +87,9 @@ string_t string_trim_end(string_t string_value) {
 }
 
 string_t string_trim(string_t string_value) {
-  string_t result = string_trim_start(string_value);
-  result = string_trim_end(result);
+  string_t result_start = string_trim_start(string_value);
+  string_t result = string_trim_end(result_start);
+  free(result_start);
   return result;
 }
 
@@ -274,16 +275,26 @@ bool string_get_has_unique_characters(const string_t string_value) {
   bool has_unique = true;
   size_t string_length = string_get_length(string_value);
   struct hash_map* characters_already_seen = hash_map_initialization();
+  string_t* keys = malloc(sizeof(string_t) * string_length);
+  for (size_t index = 0; index < string_length; index++) {
+    keys[index] = NULL;
+  }
   for (size_t index = 0; index < string_length && has_unique; index++) {
     char character = string_value[index];
-    string_t key = convert_character_to_string(character);
+    keys[index] = convert_character_to_string(character);
+    string_t key = keys[index];
     if (hash_map_contains_key(characters_already_seen, key)) {
       has_unique = false;
-      free(key);
     } else {
       hash_map_add(characters_already_seen, key, (void*)true);
     }
   }
+  for (size_t index = 0; index < string_length; index++) {
+    if (keys[index] != NULL) {
+      free(keys[index]);
+    }
+  }
+  free(keys);
   hash_map_free(characters_already_seen);
   return has_unique;
 }
@@ -315,10 +326,12 @@ bool string_get_is_substring(const string_t string_value, const string_t substri
 }
 
 string_t string_get_formatted_number(const long long number, string_t separator) {
-  string_t number_string = convert_number_to_string(number);
-  bool is_negative = number_string[0] == '-';
+  string_t number_string_temp = convert_number_to_string(number);
+  string_t number_string = number_string_temp;
+  bool is_negative = number_string_temp[0] == '-';
   if (is_negative) {
-    number_string = string_substring(number_string, 1, string_get_length(number_string));
+    number_string = string_substring(number_string_temp, 1, string_get_length(number_string_temp));
+    free(number_string_temp);
   }
   size_t number_string_length = string_get_length(number_string);
   size_t formatted_length = number_string_length + (number_string_length - 1) / 3;
@@ -343,11 +356,16 @@ string_t string_get_formatted_number(const long long number, string_t separator)
   }
   free(number_string);
   result[formatted_length] = '\0';
-  result = string_reverse(result);
+  string_t new_result = string_reverse(result);
+  free(result);
   if (is_negative) {
-    result = string_concatenate(convert_character_to_string('-'), result);
+    string_t dash = convert_character_to_string('-');
+    string_t negative_result = string_concatenate(dash, new_result);
+    free(new_result);
+    free(dash);
+    return negative_result;
   }
-  return result;
+  return new_result;
 }
 
 string_t string_get_last_occurence_of_character(const string_t string_value, char character) {