An alternative to using a StringBuilder is using LINQ with string.Join(). It's about as fast and is more concise and readable.
public string BinarySearchSetup(long[] data, long[] searchTerms)
{
var resultString = "";
var lowerBound = 0;
var upperBound = data.Length - 1;
var results = searchTerms.Select(x => BinarySearch(data, lowerBound, upperBound, x));
return string.Join(" ", results);
}
If you want to parallelize the operation, you can just call AsParallel() and then AsOrdered() to preserve order:
var results = searchTerms
.AsParallel()
.AsOrdered()
.Select(x => BinarySearch(data, lowerBound, upperBound, x));
If you want to cache the results, you can build a dictionary on the distinct elements in a similar fashion to the above LINQ query. AsOrdered() is not required because it's getting stored in a dictionary. The method will look like this:
public string BinarySearchSetup(long[] data, long[] searchTerms)
{
var lowerBound = 0;
var upperBound = data.Length - 1;
var cache = searchTerms
.Distinct()
.AsParallel()
.ToDictionary(x => x, x => BinarySearch(data, lowerBound, upperBound, x));
var results = searchTerms.Select(x => cache[x]);
return string.Join(" ", results);
}
Edit: Regarding BinarySearch(), when I make recursive methods, I like to make a top level method with less parameters that calculates the extra parameters to pass into the recursive method. Like this:
public int BinarySearch(long[] data, long key)
{
var lowerBound = 0;
var upperBound = data.Length - 1;
return BinarySearch(data, lowerBound, upperBound, key);
}
If you don't mind working with ints (which I think arrays are indexed with anyway), you can use Array.BinarySearch(). According to the documentation, a negative number is returned when an element is not found, and it's not necessarily -1, so we will have to handle that.
public longint BinarySearch(long[] data, long key)
{
int result = Array.BinarySearch(data, key);
return Math.Max(result, -1);
}
