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https://github.com/yuanqing/code-problems

:camel: Working through code problems in OCaml
https://github.com/yuanqing/code-problems

algorithms ocaml puzzles

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:camel: Working through code problems in OCaml

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# code-problems [![Build Status](https://img.shields.io/travis/yuanqing/code-problems.svg?branch=master&style=flat)](https://travis-ci.org/yuanqing/code-problems)



> Working through code problems in [OCaml](https://ocaml.org/).



Or, [parlour tricks](https://signalvnoise.com/posts/3071-why-we-dont-hire-programmers-based-on-puzzles-api-quizzes-math-riddles-or-other-parlor-tricks) for the technical interview rigmarole.



- [Problems](#problems)

  - [Data structures and algorithms](#i-data-structures-and-algorithms)

  - [Puzzles](#ii-puzzles)

- [Style guide](#style-guide)

- [Usage](#usage)

- [Known issues](#known-issues)

- [Credit](#credit)

- [License](#license)



## Problems



All the problems are in [`src/`](src), and loosely organised into categories below.



Each problem comprises a brief description, a solution program, and a test. (See [Usage](#usage) for instructions on how to build and run the tests.)



### I. Data structures and algorithms



#### Array/list



- [Binary search](src/binary_search)

- [Linked list](src/linked_list)



#### Math



- [Factorial](src/factorial)

- [Fibonacci](src/fibonacci)

- [Prime number](src/prime_number)



#### Queue



- [Queue](src/queue)

- [Queue using stacks](src/queue_using_stacks)



#### Sorting



- [Bubble sort](src/bubble_sort)

- [Insertion sort](src/insertion_sort)

- [Merge sort](src/merge_sort)

- [Quick sort](src/quick_sort)

- [Selection sort](src/selection_sort)



#### Stack



- [Stack](src/stack)

- [Stack using queues](src/stack_using_queues)



#### Tree



- [Binary search tree](src/binary_search_tree)

- [Tree traversal](src/tree_traversal)



### II. Puzzles



#### Array/list



- [Array pair sum](src/array_pair_sum)

- [Even-occurring element](src/even_occurring_element)

- [Integer difference](src/integer_difference)

- [Largest continuous sum](src/largest_continuous_sum)

- [Longest common prefix](src/longest_common_prefix)

- [Longest words](src/longest_words)

- [Missing element](src/missing_element)

- [Odd-occurring element](src/odd_occurring_element)

- [Sum of list plus one](src/sum_of_list_plus_one)

- [Sum of multiples](src/sum_of_multiples)



#### String



- [Anagram detection](src/anagram_detection)

- [Balanced brackets](src/balanced_brackets)

- [Byte format](src/byte_format)

- [Combine two strings](src/combine_two_strings)

- [CSV parse](src/csv_parse)

- [First non-repeated character](src/first_non_repeated_character)

- [Integer length](src/integer_length)

- [Largest palindrome](src/largest_palindrome)

- [Money format](src/money_format)

- [Number format](src/number_format)

- [Remove duplicate characters](src/remove_duplicate_characters)

- [Reverse words](src/reverse_words)

- [String format](src/string_format)

- [String permutations](src/string_permutations)

- [String rotation](src/string_rotation)



#### Other



- [Once](src/once)

- [Queen threatens king](src/queen_threatens_king)



## Style guide



### General practices



- Only use the [OCaml standard library](http://caml.inria.fr/pub/docs/manual-ocaml/libref/index.html).

- Memoise/cache all the things! (Or at least when we [absolutely must do so](src/fibonacci/fibonacci.ml#L2-L6), anyway.) The [`Hashtbl`](http://caml.inria.fr/pub/docs/manual-ocaml/libref/Hashtbl.html) module is your friend.

- Top-level functions should not be recursive. Instead, [use an auxiliary recursive function](src/binary_search/binary_search.ml#L2) inside the top-level function.

- If we’re writing a recursive function (which is probably most of the time), try as far as possible to write it such that it is [tail recursive](src/tree_traversal/tree_traversal.ml#L5-L27).

- For readability, annotate the arguments and return type of all top-level functions.

- Short-circuit execution by [throwing an exception](src/balanced_brackets/balanced_brackets.ml#L25-L36).

- Avoid [mutable variables](https://ocaml.org/learn/tutorials/pointers.html) if possible.



### Naming conventions



Use short variable names if we are dealing with very few variables, or if the meaning is obvious (or can be intuitively inferred). Some general conventions:



- Auxiliary function — `aux`

- List — `xs` (or `ys`, `zs`)

- Items in a list — `x` (or `y`, `z`)

- List for accumulating values — `acc`

- Binary tree — value `v` (or `w`) with a `l` subtree and a `r` subtree

- String — `str`

- Integer — `n` (or `m`)

- Length of a string or list — `len`



If there is ambiguity (eg. when we are dealing with many variables of the same type), use more descriptive names in `snake_case`.



## Usage



### Pre-requisites



- [OCaml](https://ocaml.org/) 4.02

- [OPAM](https://opam.ocaml.org) 1.2.0



### Set up



First, install [ocamlfind](https://opam.ocaml.org/packages/ocamlfind/ocamlfind.1.5.5/), [oUnit](https://opam.ocaml.org/packages/ounit/ounit.2.0.0/) (for tests), and [Bisect](https://opam.ocaml.org/packages/bisect/bisect.1.3/) (for test coverage) with OPAM:



```

$ opam install ocamlfind ounit bisect

```



Then, grab this repository:



```

$ git clone https://github.com/yuanqing/code-problems

```



### Run all the tests



```

$ cd code-problems/src

$ make

```



Use `make coverage` to run the tests and generate coverage reports (output to `coverage/`).



### Run a particular test



…for example, for the [binary search](src/binary_search) problem:



```

$ make binary_search/test

```



Use `make binary_search/coverage` to run the test and generate coverage reports (output to `coverage/`).



### Clean



To remove all compiled files and other debris:



```

$ make clean

```



## Known issues



- The [Bisect](http://bisect.x9c.fr) test coverage does not appear to be completely accurate.



## Credit



The bulk of the problems are from the [**code-problems**](https://github.com/blakeembrey/code-problems) project maintained by [Blake Embrey](https://github.com/blakeembrey).



All solution programs in this repository were written by [me](https://github.com/yuanqing).



## License



[MIT](LICENSE)