在输入为先根序列、中根序列与后根序列的前提下，对各种二叉树建树的情况进行了讨论；

As input sequences are the preorder, inorder and postorder of a binary tree, we give the discussion about creating the tree to all conditions.

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因为先要输入用户名、密码才能打开智能手机或电脑，然后再键入不同的密码打开邮箱。

First comes the user name and password needed to boot up your smartphone or computer. Next, a different password to access your E-mail.

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但任何系统要使其能对输入信号进行处理，都必须以系统稳定为先决条件。

But for any system, if the input signal will be processed, the system stability is a prerequisite.

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