Generating Random Sequences (part I)

Every once in a while, we need a random sequence. Whether to test a data structure’s performance or to run probabilistic unit tests, the provided rand primitive from your favorite programming language has several limitations. First, it’s been known for a while that if most implementations of the C standard library rand() function are not very random, despite being “good enough” in great many cases. Second, and more importantly, it does not allow you to easily control the period nor to generate a permutation on , for example.

There are many methods of generating pseudo-random number sequences. Not all exhibit the same properties and, accordingly, a method may be more useful in one case and perfectly useless in another. High quality pseudo-random number generation is a notoriously hard endeavor, but there is a number of very simple algorithms that will get you out of trouble for certain specific tasks. Let us consider, for example, the example where the pseudo-random generator must generate the numbers in exactly once, in a random order, of course, in exactly draws.

Sorting Linked Lists (part I)

The sorting algorithms we were taught in class were typically simplified versions of the algorithms that assumed that the data remained in memory and in contiguous memory locations, also known as an array. What we often have, however, are linked lists. Generalizing algorithms like the QuickSort to lists is not very hard in fact if we use a modification of the basic algorithm.

For lists with numerical keys (or values), there might be a simpler algorithm that scans the list in only one direction, so that simply linked lists are a perfectly cromulent data structure, that is, the radix sort.