二叉树的前序、中序、后序遍历的算法（递归形式和非递归形式）

//前序遍历非递归算法#define maxsize 100typedef struct {int value;Bitree *lchild;Bitree *rchild;}Bitree;typedef struct{Bitree Elem[maxsize];int top;}SqStack;void PreOrderUnrec(Bitree *t){SqStack s;StackInit(s);Bitree *p = t;while (p != NULL || !StackEmpty(s)){while (p != NULL)//遍历左子树{visit(p->data);push(s, p);p = p->lchild;}if (!StackEmpty(s))//通过下一次循环中的内嵌while实现右子树遍历  {p = pop(s);p = p->rchild;}}}//中序遍历非递归算法void InOrderUnrec(Bitree *t){SqStack s;StackInit(s);Bitree *p = t;while (p != NULL || !StackEmpty(s)){while (p != NULL)//遍历左子树{push(s, p);p = p->lchild;}if (!StackEmpty(s)){p = pop(s);visit(p->data);//访问根结点p = p->rchild; //通过下一次循环实现右子树遍历}}}//后序遍历非递归算法typedef enum{L, R} tagtype;typedef struct  {Bitree ptr;tagtype tag;}stacknode;void PostOrderUnrec(Bitree *t){SqStack s;stacknode x;StackInit(s);Bitree *p = t;do {while (p != NULL)//遍历左子树{x.ptr = p;x.tag = L;//标记为左子树push(s, x);p = p->lchild;}while (!StackEmpty(s) && s.Elem[s.top].tag == R){x = pop(s);p = x.ptr;visit(p->data);//tag为R,表示右子树访问完毕，故访问根结点}if (!StackEmpty(s)){s.Elem[s.top].tag = R;p = s.Elem[s.top].ptr->rchild;}} while (!StackEmpty(s));}//递归算法：//前序遍历：void preorder(BTree *T){//T为二叉树根结点所在链接点的地址if(T != NULL){visit(T);                 //访问T所指结点preorder(T->lchild);      //遍历T所指结点的左子树preorder(T->rchild);      //遍历T所指结点的右子树}}//中序遍历：void inorder(BTree *T){//T为二叉树根结点所在链接点的地址if(T != NULL){inorder(T->lchild);       //遍历T所指结点的左子树visit(T);                 //访问T所指结点inorder(T->rchild);       //遍历T所指结点的右子树}}//后序遍历：void postorder(BTree T){//T为二叉树根结点所在链接点的地址if(T != NULL){postorder(T->lchild);       //遍历T所指结点的左子树postorder(T->rchild);       //遍历T所指结点的右子树visit(T);                 //访问T所指结点}}