在编写代码时应尽量避免嵌套循环，目前大多数代码都是使用了哈希表、简单链表和单循环。

Your code should (almost) never have multiple nested loops (a loop inside a loop inside a loop). Most of the code written today should use Hashtables, simple lists and singly nested loops.

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理论上，哈希表是一个非常简单的构造，就是数组或链表的集合被划分到有限数量的存储体中。

In theory the hash table is a rather simple construct, just collection of arrays or linked lists divided into a finite number of buckets.

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一开始看来，用这种方法表示一个空链表使代码简单。

It may at first appear that representing empty lists in this way makes the code simpler.

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