这个问题的最佳数据结构？

Question

I am using Java for this program, and I currently have a situation where I want to add key/value pairs to a table with integer keys, like

add (1, "Bobby")
add (6, "Sue")
add (3, "Mary")
add (8, "John")
add (15, "Joe")

So naturally I want to do something like a hashtable, but when I do a lookup, if it doesn't find the exact value, I would like it to return the nearest key that isn't greater than the requested key.

So for example, if I lookup 7, it should return "Sue", but if I lookup 9, it should return "John"

I'm hoping to use one of the java util classes (HashTable, TreeMap, etc) but I'm not quite sure how to do it.

Answer 1

NavigableMap可以解决问题。

Answer 2

TreeMap from the collections library provides the functionality you're looking for

TreeMap<Integer,String> tree = new TreeMap<Integer,String>();
tree.put (1, "Bobby");
tree.put(6, "Sue");
tree.put (3, "Mary");
tree.put (8, "John");
tree.put (15, "Joe");
System.out.println(tree.floorEntry(7)); // Sue
System.out.println(tree.floorEntry(9)); // John

Answer 3

If you wanted to do this using sql something like:

select top 1 * from hashTable where keyColumnId >= @passedValueId

would work.

Answer 4

Well if you mostly read data from the structure and insert rarely you could use a trivial sorted array and do a binary search. Can't get much simpler or simpler if you're worried about search performance. Now not that great if you regularly update the structure - then you'll have to use something more complicated.

Also I think - but not totally sure - wouldn't a binary tree work just as well? Search for the position where the correct node should be and use its predecessor if the value isn't found.