Union - Intro to Computer ScienceYouTube↗  IA↗(long shot)
Education  11.1K views 14 likes 0 dislikes   29 May 2012
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so we'll have one more quiz about using
[Evans] 我们还有一个关于使用链表的小测验。
lists it will combine many of the things
它会把我们目前学到的许多知识都梳理一遍。
that we've learned after this quiz will be ready to build our web crawler so for
做完测验后，我们就可以开始建我们的网络爬虫了。
this quiz your goal is to define a procedure named Union that takes two
对于这个小测验，你的目标是定义一个名为union的过程
lists as its input it should modify the
这个过程取两个链表作为输入。
value of the first input list so when
它应修改第一个输入链表的值，
Union returns its value is now the union of the two input lists when we compute a
这样当并集返回其值时，该输入链表现在就是两个输入链表的并集了。
set Union we want to add all the
当我们计算一个集合并集时，
elements in the second list to the first
我们应把第二个链表中所有元素都加到第一个链表中，
list except if they already exist
元素已经存在的情况除外。
we shouldn't be creating any duplicate elements by adding elements that already
我们加入已经存在的元素时，不应产生重复的元素。
exist so here are a few examples so if
这里有几个例子。
you start with the variable a referring to the list 1 2 3 and the variable B
如果你从变量 a 开始，即链表1，2，3，
referring to the list 2 4 6 then we call
和变量b，即链表2，4，6，
Union passing in a and B after the call
接着我们调用并集，传入 a 和 b。
the value of a should be the list 1 2 3
调用之后，a的值应为链表1，2，3，4，6。
4 6 we've added the elements of B to a except we skipped the first element the
我们已经把 b 的元素加到了 a 中，只不过我们跳过了第一个元素，
value 2 since 2 already exists in a I
也就是值2，因为2已在 a 中。
should mention that Union should not
我要指出，并集不应修改 b 的值。
modify the value of B after the call to Union a B the value that B refers to should still be the list 2 4 6 so see if
调用了union(a,b)后，b 的值应仍为链表2，4，6。
you can define the Union procedure as described here
你试试看能否按照以上描述来定义union过程。
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