Recursive size

src/main.c

@@ -5,10 +5,10 @@
 
 int main(void) {
   Tree tree = {NULL};
-  printf("Tree size: %d\n", tree_size(&tree));
+  printf("Tree size: %d\n", tree_size(tree.root));
   tree_insert(&tree, 1);
   tree_insert(&tree, 2);
   tree_insert(&tree, 3);
-  printf("Tree size: %d\n", tree_size(&tree));
+  printf("Tree size: %d\n", tree_size(tree.root));
   return 0;
 }

src/tree.c

@@ -49,22 +49,10 @@ int tree_remove(Tree *tree, int data) { return 1; }
 
 int tree_clear(Tree *tree) { return 1; }
 
-int tree_size(Tree *tree) {
-  if (tree->root == NULL) {
+int tree_size(Node *node) {
+  if (node == NULL) {
     return 0;
   }
 
-  int size = 0;
-  Node *current = tree->root;
-  while (current != NULL) {
-    size++;
-    if (current->left != NULL) {
-      current = current->left;
-    } else if (current->right != NULL) {
-      current = current->right;
-    } else {
-      current = NULL;
-    }
-  }
-  return size;
+  return 1 + tree_size(node->left) + tree_size(node->right);
 }

src/tree.h

@@ -19,4 +19,4 @@ typedef struct Tree Tree;
 int tree_insert(Tree *tree, int data);
 int tree_remove(Tree *tree, int data);
 int tree_clear(Tree *tree);
-int tree_size(Tree *tree);
+int tree_size(Node *node);