哈希表 VS 关联数组 [英] Hash tables VS associative arrays

问题描述

最近我在一本非常著名的书算法简介".我还没有在任何实际应用程序中使用它们，但想使用.但我不知道如何开始.
谁能给我一些使用它的示例，例如，如何使用哈希表实现字典应用程序(如 ABBYY Lingvo)?
最后我想知道 PHP 中的哈希表和关联数组有什么区别，我的意思是我应该使用哪种技术以及在哪些情况下?
如果我错了(请原谅)请纠正我，因为实际上我是从哈希表开始的，而且我对它们只有基本的(理论)知识.
非常感谢.

Recently I have read about hash-tables in a very famous book "Introduction to Algorithms". I haven't used them in any real applications yet, but want to. But I don't know how to start.
Can anyone give me some samples of using it, for example, how to realize a dictionary application (like ABBYY Lingvo) using hash-tables?
And finally I would like to know what is the difference between hash-tables and associative arrays in PHP, I mean which technology should I use and in which situations?
If I am wrong (I beg pardon) please correct me, because actually I am starting with hash-tables and I have just basic (theoretical) knowledge about them.
Thanks a lot.

推荐答案

在 PHP 中，关联数组被实现为哈希表，并带有一些额外的功能.

In PHP, associative arrays are implemented as hashtables, with a bit of extra functionality.

然而，从技术上讲，关联数组与哈希表不同 - 它只是实现，部分是在幕后使用哈希表.因为它的大部分实现都是一个哈希表，所以它可以做哈希表可以做的一切——但它也可以做更多的事情.

However technically speaking, an associative array is not identical to a hashtable - it's simply implemented in part with a hashtable behind the scenes. Because most of its implementation is a hashtable, it can do everything a hashtable can - but it can do more, too.

例如，您可以使用 for 循环遍历关联数组，而使用哈希表则无法做到这一点.

For example, you can loop through an associative array using a for loop, which you can't do with a hashtable.

因此，虽然它们很相似，但关联数组实际上可以执行哈希表可以执行的超集 - 所以它们并不完全相同.将其视为哈希表加上额外的功能.

So while they're similar, an associative array can actually do a superset of what a hashtable can do - so they're not exactly the same thing. Think of it as hashtables plus extra functionality.

代码示例:

使用关联数组作为哈希表:

$favoriteColor = array();
$favoriteColor['bob']='blue';
$favoriteColor['Peter']='red';
$favoriteColor['Sally']='pink';
echo 'bob likes: '.$favoriteColor['bob']."
";
echo 'Sally likes: '.$favoriteColor['Sally']."
";
//output: bob likes blue
//        Sally likes pink

遍历关联数组:

$idTable=array();
$idTable['Tyler']=1;
$idTable['Bill']=20;
$idTable['Marc']=4;
//up until here, we're using the array as a hashtable.

//now we loop through the array - you can't do this with a hashtable:
foreach($idTable as $person=>$id)
    echo 'id: '.$id.' | person: '.$person."
";

//output: id: 1 | person: Tyler
//        id: 20 | person: Bill
//        id: 4 | person: Marc

特别注意在第二个例子中，每个元素的顺序是如何根据它们进入数组的顺序来维护的(Tyler、Bill Marc).这是关联数组和哈希表之间的主要区别.哈希表在它所持有的项目之间不保持联系，而 PHP 关联数组却可以(您甚至可以对 PHP 关联数组进行排序).

Note especially how in the second example, the order of each element is maintained (Tyler, Bill Marc) based on the order in which they were entered into the array. This is a major difference between associative arrays and hashtables. A hashtable maintains no connection between the items it holds, whereas a PHP associative array does (you can even sort a PHP associative array).

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