什么时候使用List和LinkedList更好?


当前回答

在大多数情况下,List<T>更有用。LinkedList<T>在列表中间添加/删除项时成本更低,而list <T>只能在列表末尾添加/删除项。

LinkedList<T>只有在访问顺序数据(向前或向后)时才最有效-随机访问相对昂贵,因为它每次都必须遍历链(因此它没有索引器)。但是,因为List<T>本质上只是一个数组(带有包装器),所以随机访问是可以的。

List<T>还提供了很多支持方法- Find, ToArray等;然而,这些也可以通过扩展方法用于。net 3.5/ c# 3.0的LinkedList<T> -所以这不是一个因素。

其他回答

我之前的回答不够准确。 D是正确答案 但现在我可以发布更有用和正确的答案。


我做了一些额外的检查您可以通过以下链接找到它的源代码,并在您自己的环境中通过https://github.com/ukushu/DataStructuresTestsAndOther.git重新检查它

短的结果:

Array need to use: So often as possible. It's fast and takes smallest RAM range for same amount information. If you know exact count of cells needed If data saved in array < 85000 b (85000/32 = 2656 elements for integer data) If needed high Random Access speed List need to use: If needed to add cells to the end of list (often) If needed to add cells in the beginning/middle of the list (NOT OFTEN) If data saved in array < 85000 b (85000/32 = 2656 elements for integer data) If needed high Random Access speed LinkedList need to use: If needed to add cells in the beginning/middle/end of the list (often) If needed only sequential access (forward/backward) If you need to save LARGE items, but items count is low. Better do not use for large amount of items, as it's use additional memory for links.

更多的细节:

有趣的是:

LinkedList<T> internally is not a List in .NET. It's even does not implement IList<T>. And that's why there are absent indexes and methods related to indexes. LinkedList<T> is node-pointer based collection. In .NET it's in doubly linked implementation. This means that prior/next elements have link to current element. And data is fragmented -- different list objects can be located in different places of RAM. Also there will be more memory used for LinkedList<T> than for List<T> or Array. List<T> in .Net is Java's alternative of ArrayList<T>. This means that this is array wrapper. So it's allocated in memory as one contiguous block of data. If allocated data size exceeds 85000 bytes, it will be moved to Large Object Heap. Depending on the size, this can lead to heap fragmentation(a mild form of memory leak). But in the same time if size < 85000 bytes -- this provides a very compact and fast-access representation in memory. Single contiguous block is preferred for random access performance and memory consumption but for collections that need to change size regularly a structure such as an Array generally need to be copied to a new location whereas a linked list only needs to manage the memory for the newly inserted/deleted nodes.

在. net中,列表被表示为数组。因此,与LinkedList相比,使用普通List会更快。这就是为什么上面的人看到他们看到的结果。

Why should you use the List? I would say it depends. List creates 4 elements if you don't have any specified. The moment you exceed this limit, it copies stuff to a new array, leaving the old one in the hands of the garbage collector. It then doubles the size. In this case, it creates a new array with 8 elements. Imagine having a list with 1 million elements, and you add 1 more. It will essentially create a whole new array with double the size you need. The new array would be with 2Mil capacity however, you only needed 1Mil and 1. Essentially leaving stuff behind in GEN2 for the garbage collector and so on. So it can actually end up being a huge bottleneck. You should be careful about that.

链表相对于数组的主要优点是,链接为我们提供了有效地重新排列项的能力。 塞奇威克,第91页

使用LinkedList<>时

你不知道有多少东西会通过防洪闸门。例如,令牌流。 当你只想在结尾删除\插入。

对于其他内容,最好使用List<>。

我同意上面提到的大部分观点。我也同意,在大多数情况下,List看起来是一个更明显的选择。

但是,我只是想补充一点,在很多情况下,LinkedList比List更有效。

假设你正在遍历元素,你想要执行大量的插入/删除;LinkedList在线性O(n)时间内完成,而List在二次O(n²)时间内完成。 假设你想一次又一次地访问更大的对象,LinkedList就变得非常有用。 Deque()和queue()更好地使用LinkedList实现。 当你处理很多更大的对象时,增加LinkedList的大小会更容易和更好。

希望有人会觉得这些评论有用。