O(1)空间复杂度删除一棵二叉树

删除一棵二叉树，不能递归，不能用栈，空间复杂度必须为O(1)．其思想是利用每个节点的左指针，将后序遍历中需要压入栈的节点就地连成一个链式栈。

DeleteBtree(Node* head)




...{


Node *stack = NULL;


Node *p = head->left,q;


head->left = stack;


stack = head;


while(stack != NULL)




...{


while(p != NULL)




...{


q = p;


p = q->left;


q->left = stack;


stack = q;


}


p = stack;


if(p->right != NULL)




...{


q = p;


p = q->right;


q->right = NULL; // 右子树已经访问完


}


else




...{


stack = p->left;


free(p);


p = NULL;


}


}


}