不使用栈后序遍历二叉树

 /*非递归无栈二叉树中序遍历算法*/
void InOrder2(BiTree T) {
    BiTree top=NULL,lr=NULL,r,av,
        p=T,q=T;
        /*top为栈顶指针,lr记录当前2子树结点,r为临时变量,
    av为当前可用叶子结点,p为当前访问结点,q为p的父亲结点*/
    if(T==NULL) return ;
    while(1) { /*向下访问搜索*/
        while(1) {
            if(p->lchild==NULL&&p->rchild==NULL) {/*如果访问到底，就输出该结点*/
                printf("%c ",p->data);
                break;
            }
            else if(p->lchild==NULL) {/*沿左子树访问到底，转向访问右子树*/
                printf("%c ",p->data);
                r=p->rchild;
                p->rchild=q;
                q=p; p=r;
            }
            else {/*一直沿左子树访问下去*/
                r=p->lchild;
                p->lchild=q;
                q=p; p=r;
            }
        }
        av=p;/*p为叶子结点，av记录当前叶子结点*/
        while(1) {
            if(p==T) return;/*如果回退到根，返回*/
                            else if(q->lchild==NULL) {/*如果父结点q的lchild为空，
                                表示p为q的右儿子*/
                                r=q->rchild; /*向父结点的右儿子方向回退*/
                                q->rchild=p; /*重新连接父指针*/
                                p=q; q=r;
                            }
                            else if(q->rchild==NULL) {/*类似上面*/
                                r=q->lchild;
                                q->lchild=p;
                                p=q; q=r;
                                printf("%c ",p->data);
                            }
                            else {/*如果p的父亲q有两个子树,用以下方法判断p是q的左儿子还是右儿子*/
                                if(q==lr) {/*p是q的右儿子*/
                                    r=top; /*退栈*/
                                    lr=r->lchild; /*lchild相当于链表的data域，rchild相当next域*/
                                    top=r->rchild;
                                    r->lchild=r->rchild=NULL;/*退栈结束*/
                                    r=q->rchild;
                                    q->rchild=p;
                                    p=q; q=r;
                                }
                                else { /*p是q的左儿子*/
                                    printf("%c ",q->data);
                                    av->lchild=lr;/*入栈加回退操作*/
                                    av->rchild=top;
                                    top=av; lr=q;
                                    r=q->lchild;
                                    q->lchild=p;
                                    p=q->rchild;
                                    q->rchild=r;
                                    break;
                                }
                            }
        }
    }
   
}