Structure to use for between values - something like a HashMap

Question

I want to know what will be best to use if I have something like chapters with pages from-to - example:

Chapter 1, 0-10;
Chapter 2, 11-33;
Chapter 3, 54-90;
...

Now I want to get the chapter based on the on a page number, in example I input 60, and it should return Chapter 3.

How can I do this in JAVA?

Use a `NavigableMap`, and the `floorKey()` method: http://www.tutorialspoint.com/java/util/treemap_floorkey.htm — Kon, Mar 11 '15 at 14:31
Depends on your principal requirement, speed or memory cost. For absolute speed, a simple HashMap with every page as a key and their chapter as the value would be best. — initramfs, Mar 11 '15 at 14:34
Use `TreeMap` look at answer of http://stackoverflow.com/questions/1314650/using-java-map-for-range-searches — user370305, Mar 11 '15 at 14:36
@Darko Petkovski - Are they continues page number for chapters? LIke, for Chapter 3 its should be 34 not 54 ?? — user370305, Mar 11 '15 at 14:47
Do you want the hashmap to return a string or an integer Darko — Xjasz, Mar 11 '15 at 14:52
These hashmaps are just name value pairs darko. You can make them however you want. If you want 34 to return chapter 3. Its as simple as this chapters.put(34, "Chapter3"); now you can change the chapters to ints if you want I just thought I would make it simple to understand. — Xjasz, Mar 11 '15 at 14:56

Xjasz · Answer 1 · 2015-03-11T15:40:22.310

-1

You could make a hash map of Integers that return a String for the chapter you are on

private void SimpleChapterHashmap(){
    HashMap<Integer, Integer> chapters = new HashMap<Integer, Integer>();
    for (int i = 0; i < 10; i++) {
        chapters.put(i, 1);
    }
    for (int i = 11; i < 33; i++) {
        chapters.put(i, 2);
    }
    for (int i = 34; i < 90; i++) {
        chapters.put(i, 3);
    }

    Log.d("CHAPTER", chapters.get(60));
}

edited Mar 11 '15 at 15:40

answered Mar 11 '15 at 14:35

Xjasz

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Its just an example this isn't something that oracle needs. – Xjasz Mar 11 '15 at 14:38
@Xjasz See my comment above for a MUCH better, MUCH more efficient implementation which is already part of the Java API – Kon Mar 11 '15 at 14:48
Your link is no different other than using – Xjasz Mar 11 '15 at 14:51
I think the reason people are saying it's inefficient is not because you used `String` but because you stored an entry for every page rather than every chapter. All the other people commenting have assumed the `54` in the question was a typo, and that you could use a `TreeMap` to just store the last page number for each chapter. In fairness, your answer does answer the question as given. – Paul Boddington Mar 11 '15 at 15:03
I was only using a String to help him understand it a little better. Of course you can use integer,integer or even range,integer but that might make it harder for someone to understand. – Xjasz Mar 11 '15 at 15:06

Structure to use for between values - something like a HashMap

1 Answers1