Random number generator without duplicates java
Rating:
5,2/10
913
reviews

However, 2 32 is not a prime number. The intermediateOffset variable acts as a seed, putting a variety of different sequences at our disposal. You can just add new numbers to the set as you need to generate them. You won't notice a difference, but the array will preserve insertion order. I think we all agree about what the original poster wanted; it's just what you call it. Good idea about a Set.

Regarding seetharaman venkatasamy's example: umm, huh? Do you know any other way to solve this problem? Right - it's not supposed to. In fact, the of unique values in such sequences is only about 9988367. One other way would be to generate the 1000 values into a Set and pick 50 from them and you remove one each time you pick it from the set. In an attempt to span the available range of 32-bit values, we could even model the initial sequence as a. . If you eventually need to generate all or even most of the possible values, then a shuffle is probably a better choice.

One naive approach which would work would be to create a Set and until its size is not 50 loop to add another random number. How can we do it? This point is often heavily emphasized in introductory probability courses, to dislodge certain types of fallacious thinking that students may arrive with. That's fine - the fact that it's not an even distribution across all numbers in the range, period, does not mean it's not random. It also passes tests in the more stringent Crush suite. Keep trying until you generate a random number that's not in the set.

Simple add the numbers to a Set, for example a HashSet, which cannot contain duplicate values, until your Set hat the desired length. You won't notice a difference, but the array will preserve insertion order. But if you put random numbers into a Set, and extract them, which order do you get them back in? It's a good choice if the total number of random numbers needed is small compared to the range of possible values. It just means it doesn't match one particular concept of a random distribution. What would happen if we used TreeSet instead? I altered the little program I posted earlier to try a LinkedHashSet, and only that maintains insertion order with the for-each loop. Any help would be appreciated. You still need to allocate an array big enough to store all the values, but as long as that's not more memory than you have available, I believe this strategy would be the fastest one possible, overall.

If we come up with a good permutation, all we need is to call it with increasing inputs { 0, 1, 2, 3, â€¦ }. Another way is to generate random numbers, storing them in a Set, until the Set is large enough; the Set, by its nature, will eliminate duplicates. Suppose we wish to generate a sequence of 10000000 random 32-bit integers with no repeats. As a compromise, we can write a C++ function which permutes all integers below this prime, and simply maps the 5 remaining integers to themselves. Actually even HashSet doesn't seem to print in insertion order. If that other element is also the same element, there's really nothing to do.

Incidentally, it's also possible to modify the shuffle algorithm so that you don't shuffle the entire list at once. The index would tell us which free slot to take next. Instead you can just pick out one number at a time, randomly chosen from the remaining numbers, as needed. Each time you generate a new random number, if it's already in the set. Here's an implementation of what I was thinking of.

I faced this problem recently, and considered several options before finally implementing a custom, non-repeating pseudo-random number generator which runs in O 1 time, requires just 8 bytes of storage, and has pretty good distribution. Or, instead of starting with an array of all possible 32-bit integers, we could start with an initial sequence of any 10000000 sorted integers. I understand there are ways like put those in a List structure and shuffle, but could I done it with Random generator? There are many types of random distributions. Purely random numbers, with no other stated constraints, would not be influenced by past behavior, true. We could even begin the input sequence at any value. Random is described as pseudo-random , is there any need to shuffle the array? In this case, it's an even distribution across all numbers in a given range that have not previously been selected. Not that you need to rely on insertion order behavior if you use the strategy I just described, but for the fill-the-set-then-remove-items strategy, it could be useful.

We're generating random numbers, subject to the constraint that there can be no duplicates. So there is no way tell the next nextInt call to generate a number that has not been generated yet. Hm, I didn't really follow this part. Let's say I want to generate 25 random numbers on a 8 by 6 grid. If the input is random and java. Using this approach, we could begin with an array containing all possible 32-bit integers, and shuffle the first 10000000 values out of the array to obtain our sequence. A LinkedHashSet would do the job though.

If you wanted, you could probably adapt it to work on ranges of integers other than 2 32 as well. Random is described as pseudo-random , is there any need to shuffle the array? In other words, a repeating cycle of 2 32 values. You don't need to extract them, or pre-generate the set. I understand that Random is pseudo-random; I haven't been bothering to make that distinction, but it's true. Aside from that though I don't think I understand the scenario you're talking about.