1 files changed, 34 insertions, 2 deletions

diff --git a/tree.c b/tree.c
index b2515ca..9dc9cb9 100644
--- a/tree.c
+++ b/tree.c
@@ -554,6 +554,38 @@ tree_iterator_free(struct tree_iterator *it)
         stack_free(&it->stack);
 }
 
+struct tree_node *
+tree_preorder_iterator_next(struct tree_iterator *it)
+{
+        struct tree_node *node = NULL;
+
+        if ( stack_pop(&it->stack, &node) ) {
+                if ( node->right != NULL ) {
+                        stack_push(&it->stack, node->right);
+                }
+                if ( node->left != NULL ) {
+                        stack_push(&it->stack, node->left);
+                }
+        }
+
+        return node;
+}
+
+struct tree_node *
+tree_preorder_iterator_first(struct tree_iterator *it, struct tree_node *tree)
+{
+        stack_init(&it->stack);
+
+        if ( tree ) {
+                stack_push(&it->stack, tree);
+
+                return tree_preorder_iterator_next(it);
+        }
+        else {
+                return NULL;
+        }
+}
+
 /* ===== */
 
 void
@@ -656,11 +688,11 @@ main(void)
         show_tree(tree, 0, 0);
 
         struct tree_iterator it;
-        struct tree_node *   node = tree_iterator_first(&it, tree);
+        struct tree_node *   node = tree_preorder_iterator_first(&it, tree);
         while ( node ) {
                 fprintf(stdout, "%d\n", node->key);
 
-                node = tree_iterator_next(&it);
+                node = tree_preorder_iterator_next(&it);
         }
         tree_iterator_free(&it);