Algorithm to find times when resources are available

What you actually want to test here, I assume, is that given a specific set of results from the randomiser, the rest of your method performs correctly.

If that's what you're looking for then mock out the randomiser, to make it deterministic within the realms of the test.

I generally have mock objects for all kinds of non-deterministic or unpredictable (at the time of writing the test) data, including GUID generators and DateTime.Now.

Edit, from comments: You have to mock the PRNG (that term escaped me last night) at the lowest level possible - ie. when it generates the array of bytes, not after you turn those into Int64s. Or even at both levels, so you can test your conversion to an array of Int64 works as intended and then test separately that your conversion to an array of DateTimes works as intended. As Jonathon said, you could just do that by giving it a set seed, or you can give it the array of bytes to return.

I prefer the latter because it won't break if the framework implementation of a PRNG changes. However, one advantage to giving it the seed is that if you find a case in production that didn't work as intended, you only need to have logged one number to be able to replicate it, as opposed to the whole array.

All this said, you must remember that it's called a Pseudo Random Number Generator for a reason. There may be some bias even at that level.

1. Include all the start and end points (in time) of the Jobs in an array (this creates 2*N elements (1 for start 1 for end))
2. sort the array ordering by the timestamp of the event,

3. then iterate over the (2*N) elements as follows:

   for each element X 
   do 
     if(X.type == start)
       counter++
     else
       counter--
     ans=max(ans, counter);
   end
   

Complexity: O(n.log(n)) for initial build of the sorted structure + O(n) for the iteration through its elements.

Edit: It has been suggested by Giorgio that an array is used, which is a better option. (The suggestion originally was to use a red/black tree, but no task removing capability seems to be needed, so maintaining order is trivial).