复制二叉树（非递归实现）:
pbinary_tree_node copy_binary_tree(pbinary_tree_node bt)
{//先序遍历输出一颗树的全部结点值1,2,3
stack<pbinary_tree_node> stack_left,stack_right;
pbinary_tree_node newbt;
if (bt!=NULL)
{
//new root
newbt=new binary_tree_node;
newbt->data=bt->data;
//travel bt and travel newbt at the same time
stack_left.push(bt);
stack_right.push(newbt);
