Added helper method to allocate nodes from the vector for me

The vector acts as an arena for the nodes to be allocated from, better
and faster than allocating each child on the heap individually.

src/main.cpp

@@ -87,6 +87,13 @@ struct Node
 };
 
 std::vector<Node> nodes;
+
+Node *alloc_node(Node n)
+{
+  nodes.push_back(n);
+  return nodes.data() + (nodes.size() - 1);
+}
+
 std::queue<Node *> to_iterate;
 
 void iterate(void)
@@ -97,17 +104,15 @@ void iterate(void)
   to_iterate.pop();
   if (!node->left)
   {
-    Node new_node = Fraction{node->value.numerator,
-                             node->value.numerator + node->value.denominator};
-    nodes.push_back(new_node);
-    node->left = nodes.data() + (nodes.size() - 1);
+    node->left =
+        alloc_node(Fraction{node->value.numerator,
+                            node->value.numerator + node->value.denominator});
   }
   else if (!node->right)
   {
-    Node new_node = Fraction{node->value.numerator + node->value.denominator,
-                             node->value.denominator};
-    nodes.push_back(new_node);
-    node->right = nodes.data() + (nodes.size() - 1);
+    node->right =
+        alloc_node(Fraction{node->value.numerator + node->value.denominator,
+                            node->value.denominator});
   }
   to_iterate.push(node->left);
   to_iterate.push(node->right);