void PostBtree(BTree & t, string mid, string post, int lm, int
rm, int lp, int rp);
void PreBtree(BTree & t, string mid, string pre, int lm, int
rm, int lp, int rp);
void Preorder(BTree p); //先序遍历
void Postorder(BTree p); //后序遍历
int main(int argc, char* argv[])
{
string pre, mid, post;