Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I think your implementation of mergeSort doesn't scale very well. You are using your <code>copy</code> method to copy the appropriate range of the input list as input for a recursive call to <code>mergeSort</code>. If you consider the whole depth of the recursion, you need additional space the size of the entire input list on each level.</p> <p>This means your code needs memory of log2(n) times n where n is the size of your input list. If you are about to mergeSort a list of size 65'536 elements, your code will create copies of it such that it will use a peak amount of log2(65'536) = 16 times the memory requirements of your input table. This might very well lead to a <code>StackOverflowException</code>.</p> <p>To remedy this, I'd rewrite the <code>mergeSort</code> method (or rather create an overloaded version of it) to accept a list together with lower and upper bounds pointing into the list. That way, you won't need to copy the list on each recursion step. On the other hand, as soon as the range delimited by the lower and upper bounds contains just one element, you return a new <code>List</code> containing just this single element which <code>merge()</code> will operate on. That way, you only copy the whole input list once (i.e. at the lowest recursion level), and you'll end up using only twice the memory that the input list occupies (in complexity terms, <code>O(n)</code>). As soon as <code>merge()</code> will have passed over these single-element-lists and will have created a new intermediate result list, the single-element-lists will be available for GC.</p>
    singulars
    1. This table or related slice is empty.
    1. POmergeSort with List interface
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USMarcellus
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POmergeSort with List interface
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COThanks that implementation is very cool and I will implement it in my code, but right now Im randomly getting a stack overflow with data that contains only 10 objects. Sometimes it will not have a stack overflow and run, but when it does the objects are not sorted, so there must be a logic error. Im confused because people said it worked for them, did it just run with out errors for them or did it actually sort the data for them? Thanks!
      singulars
      1. PO
      1. USJohn
    2. COHm, you're having stack overflows with only 10 objects? That's really odd, the only cause for this I can imagine would be some accidental infinite loop happening in the code. But your divide step and choosing of indexes looks reasonable, and also the while loop in the merge step seems to be certain to terminate... Are you sure this code is the cause for the stack overflow and not something around it?
      singulars
      1. PO
      1. USMarcellus
    3. COk, please forget what I just said. The stack overflow is being caused by the subsequent binary search, which makes sense because it expects a sorted list and if the merge sort is not working properly the binary wont either. So I guess the only problem I have now is that the algorithm isn't actually working, it has some kind of logic error.
      singulars
      1. PO
      1. USJohn
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload