typedef struct tree$\_$node $\{$

shape$\_$t$*$ shape; $//$ Shape associated with the node

struct tree$\_$node$*$ left; $//$ Left subtree

struct tree$\_$node$*$ right; $//$ Right subtree

$\}$ tree$\_$node$\_$t;

#define MAX$\_$DEPTH $30$

typedef struct $\{$

tree$\_$node$\_$t$*$ curr; $//$ Pointer to the current node

unsigned int depth; $//$ Current depth in the tree $($root is at depth $0)$

tree$\_$node$\_$t$*$ parents$[$MAX$\_$DEPTH$]$; $//$ Pointer to parent nodes

$\}$ tree$\_$iterator$\_$t; $//$ Helper struct for iterating through a tree $--$ represents a current location within the tree