# Binary Search in Elixir

#### Implement a binary search algorithm.

1 | ```
exercism fetch elixir binary-search
``` |

# Binary Search

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.

## Running tests

Execute the tests with:

1 |
```
$ elixir bob_test.exs
``` |

(Replace `bob_test.exs`

with the name of the test file.)

### Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by
commenting out the relevant `@tag :pending`

with a `#`

symbol.

For example:

Or, you can enable all the tests by commenting out the
`ExUnit.configure`

line in the test suite.

1 |
```
# ExUnit.configure exclude: :pending, trace: true
``` |

For more detailed information about the Elixir track, please see the help page.

## Source

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

## Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.