带索引检索的排序数据结构

Question

Which Collection stores data in some specified order and can return or set elements according to index? I know that TreeSet implements SortedSet, hence stores data according to either natural ordering or some Comparator object provided by the programmer. But I don't know how to retrieve or set elements in a TreeSet using index. On the other hand, ArrayList and some other structures can be used to retrieve or set their elements accoring to any index. But they don't store elements in sorted order. Any way to have both features?

Answer 1

You can just use an ArrayList and sort it using Collections.sort . If you have to insert elements, you can find the insertion-point using Collections.binarySearch , giving you O(log n) complexity for insertions (as opposed to O(n log n) for resorting). ArrayList provides an overload of add that takes a position parameter .

Answer 2

Take a look at indexed-tree-map https://github.com/geniot/indexed-tree-map I enhanced TreeMap to provide access and retrieval by index. To get the insertion index of a key which doesn't exist you can try to run the put-entryIndex-remove sequence. Although it may not be very efficient for your requirements. My entryIndex implementation is based on first finding the entry and then calculating its index. I will take a look if it can be improved for non-existing keys.

You can't set elements by index in a sorted set without breaking accidentally the sorting order. If you mean 'setting values of a map by key's index' then again you can use index-tree-map. Just find the key by index and use put to overwrite the value.

Answer 3

将元素填充到 ArrayList 中并通过调用 Collections.sort() 对其进行排序。