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I'm looking at List and I see a BinarySearch method with a few overloads, and I can't help wondering if it makes sense at all to have a method like that in List?
Why would I want to do a binary search unless the list was sorted? And if the list wasn't sorted, calling the method would just be a waste of CPU time. What's the point of having that method on List?
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Binary search works by assuming the middle of the array contains the median value in the array. If it is not sorted, this assumption does not make sense, since the median can be anywhere and cutting the array in half could mean that you cut off the number you were searching for.
BinarySearch(Array, Object) Searches an entire one-dimensional sorted array for a specific element, using the IComparable interface implemented by each element of the array and by the specified object.
Binary search is an efficient algorithm for finding an item from a sorted list of items. It works by repeatedly dividing in half the portion of the list that could contain the item, until you've narrowed down the possible locations to just one. We used binary search in the guessing game in the introductory tutorial.
Binary search compares the target value to the middle element of the array. If they are not equal, the half in which the target cannot lie is eliminated and the search continues on the remaining half, again taking the middle element to compare to the target value, and repeating this until the target value is found.
I note in addition to the other correct answers that binary search is surprisingly hard to write correctly. There are lots of corner cases and some tricky integer arithmetic. Since binary search is obviously a common operation on sorted lists, the BCL team did the world a service by writing the binary search algorithm correctly once rather than encouraging customers to all write their own binary search algorithm; a significant number of those customer-authored algorithms would be wrong.
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