Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Ok so you are given input as follows:</p> <pre><code>(3, 7) (1, 2) (2, 5) (4, 1) (5, 2) </code></pre> <p>And you want to pick a random number so that the weight of each id is reflected in the picking, i.e. pick a random number from the following list:</p> <pre><code>3 3 3 3 3 3 3 1 1 2 2 2 2 2 4 5 5 </code></pre> <p>Initially, I created a temporary array but this can be done in memory as well, you can calculate the size of the list by summing all the weights up = X, in this example = 17</p> <p>Pick a random number between [0, X-1], and calculate which which id should be returned by looping through the list, doing a cumulative addition on the weights. Say I have a random number 8</p> <pre><code>(3, 7) total = 7 which is &lt; 8 (1, 2) total = 9 which is &gt;= 8 **boom** 1 is your id! </code></pre> <p>Now since you need K random <strong>unique</strong> ids you can create a hashtable from initial array passed to you to work with. Once you find an id, remove it from the hash and proceed with algorithm. <strong>Edit</strong> Note that you create the hashmap initially only once! You algorithm will work on this instead of looking through the array. I did not put in in the top to keep the answer clear</p> <p>As long as your random calculation is not using any extra memory secretly, you will need to store K random pickings, which are &lt;= N and a copy of the original array so max space requirements at runtime are O(2*N)</p> <p>Asymptotic runtime is :</p> <pre><code>O(n) : create copy of original array into hastable + ( O(n) : calculate sum of weights + O(1) : calculate random between range + O(n) : cumulative totals ) * K random pickings = O(n*k) overall </code></pre> <p>This is a good question :)</p>
    singulars
    1. This table or related slice is empty.
    1. POC++: function creation using array
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USVictor Parmar
    1. USVictor Parmar
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    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. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO@Vic doesn't "create copy of original array into hastable" break the requirement " ammount of memory allocated should be known at compile time, i.e. no additional memory should be allocated"
      singulars
      1. PO
      1. USConrad Frix
    2. COIt's O(NK), and you're allocating memory for the hash table which OP says isn't allowed (I presume he means O(1) space).
      singulars
      1. PO
      1. USmarcog
    3. COWell they want K numbers returned, where are you going to put them? I think the idea is that they want to have a constant maximum amount of memory that the function can allocate and it won't grow beyond the hashmap + the array to store the ids, which should be O(2*N).
      singulars
      1. PO
      1. USVictor Parmar
 

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