revert a list

linked-list.c

@@ -81,9 +81,36 @@ void list_remove(list_t * list, list_node_t * item) {
   }
 }
 
-/* FIXME
- * list_node_t list_revert(list_node_t *list) {
-} */
+void list_revert(list_t *list) {
+  list_t reverted;
+  reverted.head = NULL;
+
+  list_node_t *cur = list->head;
+  while (cur != NULL) {
+    list_node_t *next = cur->next;
+    list_node_t *headbefore = reverted.head;
+
+    reverted.head = cur;
+    cur->next = headbefore;
+
+    cur = next;
+  }
+
+  list->head = reverted.head;
+}
+
+list_node_t* list_elementat(list_t *list, int i) {
+  if (i > list_length(list)-1) {
+    return NULL;
+  }
+
+  list_node_t *cur = list->head;
+  for (int j=0; j < i; j++) {
+    cur = cur->next;
+  }
+
+  return cur;
+}
 
 int main(int argc, char *argv[]) {
   list_t *emptylist = malloc(sizeof(list_t));
@@ -167,4 +194,35 @@ int main(int argc, char *argv[]) {
   assert(list_empty(foolist) == true);
   list_print(foolist);
   printf("list_length = %d\n", list_length(foolist));
+
+  /* revert a list */
+  const int howmany2 = 10;
+  for (int i = 0; i < howmany2; i++) {
+    list_node_t *newnode = malloc(sizeof(list_node_t));
+    newnode->data = i;
+
+    list_add(foolist, newnode);
+  }
+
+  for (int i = 0; i < howmany2; i++) {
+    list_node_t *el = list_elementat(foolist, i);
+    assert(el->data == i);
+  }
+
+  assert(list_length(foolist) == howmany2);
+  list_print(foolist);
+  printf("list_length = %d\n", list_length(foolist));
+
+  list_revert(foolist);
+
+  for (int i = 0; i < howmany2; i++) {
+    list_node_t *el = list_elementat(foolist, i);
+    assert(el->data == howmany2-i-1);
+  }
+
+  assert(list_length(foolist) == howmany2);
+  list_print(foolist);
+  printf("list_length = %d\n", list_length(foolist));
+
+  /* FIXME: frees */
 }