Binary Search

Welcome to Binary Search on Exercism's Rust Track. If you need help running the tests or submitting your code, check out HELP.md.

Instructions

Implement a binary search algorithm.

Searching a sorted collection is a common task. A dictionary is a sorted list of word definitions. Given a word, one can find its definition. A telephone book is a sorted list of people's names, addresses, and telephone numbers. Knowing someone's name allows one to quickly find their telephone number and address.

If the list to be searched contains more than a few items (a dozen, say) a binary search will require far fewer comparisons than a linear search, but it imposes the requirement that the list be sorted.

In computer science, a binary search or half-interval search algorithm finds the position of a specified input value (the search "key") within an array sorted by key value.

In each step, the algorithm compares the search key value with the key value of the middle element of the array.

If the keys match, then a matching element has been found and its index, or position, is returned.

Otherwise, if the search key is less than the middle element's key, then the algorithm repeats its action on the sub-array to the left of the middle element or, if the search key is greater, on the sub-array to the right.

If the remaining array to be searched is empty, then the key cannot be found in the array and a special "not found" indication is returned.

A binary search halves the number of items to check with each iteration, so locating an item (or determining its absence) takes logarithmic time. A binary search is a dichotomic divide and conquer search algorithm.

Restrictions

Rust provides in its standard library already a binary search function. For this exercise you should not use this function but just other basic tools instead.

Hints

Slices have additionally to the normal element access via indexing (slice[index]) many useful functions like split_at or getting subslices (slice[start..end]).

You can solve this exercise by just using boring old element access via indexing, but maybe the other provided functions can make your code cleaner and safer.

For bonus points

Did you get the tests passing and the code clean? If you want to, there are some additional things you could try.

Currently your find function will probably only work for slices of numbers, but the Rust type system is flexible enough to create a find function which works on all slices which contains elements which can be ordered.
Additionally this find function can work not only on slices, but at the same time also on a Vec or an Array.

To run the bonus tests, remove the #[ignore] flag and execute the tests with the generic feature, like this:

$ cargo test --features generic

Then please share your thoughts in a comment on the submission. Did this experiment make the code better? Worse? Did you learn anything from it?

Hints for Bonus Points

To get your function working with all kind of elements which can be ordered, have a look at the Ord Trait.
To get your function working directly on Vec and Array, you can use the AsRef Trait

Source

Created by

@shybyte

Contributed to by

@Cohen-Carlisle
@coriolinus
@cwhakes
@efx
@ErikSchierboom
@lutostag
@nfiles
@petertseng
@rofrol
@stringparser
@xakon
@ZapAnton

Based on

Wikipedia - http://en.wikipedia.org/wiki/Binary_search_algorithm

3.8 KiB Raw Permalink Blame History