A binary search needs the max and min boundaries of the search. Starting at zero is great, but your last variable is a little off. Try: last=$(($#students[@]} – 1)) the – 1 will put your array at the correct size (arrays start at zero and go to one less of their size.) After that try … Read more
It would be much better to work with a lower and upper indexes as Lasse V. Karlsen was suggesting in a comment to the question. This would be the code: def binary_search(array, target): lower = 0 upper = len(array) while lower < upper: # use < instead of <= x = lower + (upper – … Read more
I doubt there is a general purpose binary search method in .NET like that, except for the one being present in some base classes (but apparently not in the interfaces), so here’s my general purpose one. public static Int32 BinarySearchIndexOf<T>(this IList<T> list, T value, IComparer<T> comparer = null) { if (list == null) throw new … Read more
Well, you can make it work in lots of ways, but: 1) I use low=0, high=arr.length. If I’m going to call variables low and high, then I want low<=high always, even at the end of the search. This is also easier to think about when arr.length==0 2) while (low<high). This corresponds to the answer for … Read more
This post covers this famous bug in a lot of detail. As others have said it’s an overflow issue. The fix recommended on the link is as follows: int mid = low + ((high – low) / 2); // Alternatively int mid = (low + high) >>> 1; It is also probably worth mentioning that … Read more
Ensure that your array is sorted since this is the crux of a binary search. Any indexed/random-access data structure can be binary searched. So when you say using “just an array”, I would say arrays are the most basic/common data structure that a binary search is employed on. You can do it recursively (easiest) or … Read more
Here a more mathematical way of seeing it, though not really complicated. IMO much clearer as informal ones: The question is, how many times can you divide N by 2 until you have 1? This is essentially saying, do a binary search (half the elements) until you found it. In a formula this would be … Read more
There is no such functions, but you can write a simple one using std::lower_bound, std::upper_bound or std::equal_range. A simple implementation could be template<class Iter, class T> Iter binary_find(Iter begin, Iter end, T val) { // Finds the lower bound in at most log(last – first) + 1 comparisons Iter i = std::lower_bound(begin, end, val); if … Read more
There are a bunch of little things you have to get right in a binary search: handle the length=0 case, make sure the position you test is always valid, make sure you don’t overflow (i.e., `(low+high)/2′ is not the best way to write that), make sure the new test position is always different from the … Read more
It’s useful to write a search function in such a way that it returns a negative value indicating the insertion point for the new element if the element is not found. Also, using recursion in a binary search is excessive and unnecessary. And finally, it’s a good practice to make the search algorithm generic by … Read more