Use reference links in descriptions (#2113)

Author: kytrinyx

exercises/all-your-base/description.md

@@ -10,7 +10,7 @@ represented as a sequence of digits, convert it to base **b**.
 - Try to implement the conversion yourself.
   Do not use something else to perform the conversion for you.
 
-## About [Positional Notation](https://en.wikipedia.org/wiki/Positional_notation)
+## About [Positional Notation][positional-notation]
 
 In positional notation, a number in base **b** can be understood as a linear
 combination of powers of **b**.
@@ -30,3 +30,5 @@ The number 1120, *in base 3*, means:
 I think you got the idea!
 
 *Yes. Those three numbers above are exactly the same. Congratulations!*
+
+[positional-notation]: https://en.wikipedia.org/wiki/Positional_notation

exercises/alphametics/description.md

@@ -2,8 +2,7 @@
 
 Write a function to solve alphametics puzzles.
 
-[Alphametics](https://en.wikipedia.org/wiki/Alphametics) is a puzzle where
-letters in words are replaced with numbers.
+[Alphametics][] is a puzzle where letters in words are replaced with numbers.
 
 For example `SEND + MORE = MONEY`:
 
@@ -30,3 +29,5 @@ Each letter must represent a different digit, and the leading digit of
 a multi-digit number must not be zero.
 
 Write a function to solve alphametics puzzles.
+
+[Alphametics]: https://en.wikipedia.org/wiki/Alphametics

exercises/armstrong-numbers/description.md

@@ -1,6 +1,6 @@
 # Description
 
-An [Armstrong number](https://en.wikipedia.org/wiki/Narcissistic_number) is a number that is the sum of its own digits each raised to the power of the number of digits.
+An [Armstrong number][armstrong-number] is a number that is the sum of its own digits each raised to the power of the number of digits.
 
 For example:
 
@@ -10,3 +10,5 @@ For example:
 - 154 is *not* an Armstrong number, because: `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
 
 Write some code to determine whether a number is an Armstrong number.
+
+[armstrong-number]: https://en.wikipedia.org/wiki/Narcissistic_number

exercises/connect/description.md

@@ -2,8 +2,7 @@
 
 Compute the result for a game of Hex / Polygon.
 
-The abstract boardgame known as
-[Hex](https://en.wikipedia.org/wiki/Hex_%28board_game%29) / Polygon /
+The abstract boardgame known as [Hex][] / Polygon /
 CON-TAC-TIX is quite simple in rules, though complex in practice. Two players
 place stones on a parallelogram with hexagonal fields. The player to connect his/her
 stones to the opposite side first wins. The four sides of the parallelogram are
@@ -29,3 +28,5 @@ The boards look like this:
 "Player `O`" plays from top to bottom, "Player `X`" plays from left to right. In
 the above example `O` has made a connection from left to right but nobody has
 won since `O` didn't connect top and bottom.
+
+[Hex]: https://en.wikipedia.org/wiki/Hex_%28board_game%29

exercises/darts/description.md

@@ -2,8 +2,8 @@
 
 Write a function that returns the earned points in a single toss of a Darts game.
 
-[Darts](https://en.wikipedia.org/wiki/Darts) is a game where players
-throw darts at a [target](https://en.wikipedia.org/wiki/Darts#/media/File:Darts_in_a_dartboard.jpg).
+[Darts][] is a game where players
+throw darts at a [target][darts-target].
 
 In our particular instance of the game, the target rewards 4 different amounts of points, depending on where the dart lands:
 
@@ -12,6 +12,12 @@ In our particular instance of the game, the target rewards 4 different amounts o
 * If the dart lands in the middle circle of the target, player earns 5 points.
 * If the dart lands in the inner circle of the target, player earns 10 points.
 
-The outer circle has a radius of 10 units (this is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered at the same point (that is, the circles are [concentric](http://mathworld.wolfram.com/ConcentricCircles.html)) defined by the coordinates (0, 0).
+The outer circle has a radius of 10 units (this is equivalent to the total radius for the entire target), the middle circle a radius of 5 units, and the inner circle a radius of 1. Of course, they are all centered at the same point (that is, the circles are [concentric][] defined by the coordinates (0, 0).
 
-Write a function that given a point in the target (defined by its [Cartesian coordinates](https://www.mathsisfun.com/data/cartesian-coordinates.html) `x` and `y`, where `x` and `y` are [real](https://www.mathsisfun.com/numbers/real-numbers.html)), returns the correct amount earned by a dart landing at that point.
+Write a function that given a point in the target (defined by its [Cartesian coordinates][cartesian-coordinates] `x` and `y`, where `x` and `y` are [real][real-numbers]), returns the correct amount earned by a dart landing at that point.
+
+ [Darts]: https://en.wikipedia.org/wiki/Darts
+ [darts-target]: https://en.wikipedia.org/wiki/Darts#/media/File:Darts_in_a_dartboard.jpg
+ [concentric]: http://mathworld.wolfram.com/ConcentricCircles.html
+ [cartesian-coordinates]: https://www.mathsisfun.com/data/cartesian-coordinates.html
+ [real-numbers]: https://www.mathsisfun.com/numbers/real-numbers.html

exercises/dot-dsl/description.md

@@ -1,16 +1,15 @@
 # Description
 
-A [Domain Specific Language
-(DSL)](https://en.wikipedia.org/wiki/Domain-specific_language) is a
+A [Domain Specific Language (DSL)][dsl] is a
 small language optimized for a specific domain. Since a DSL is
 targeted, it can greatly impact productivity/understanding by allowing the
 writer to declare *what* they want rather than *how*.
 
 One problem area where they are applied are complex customizations/configurations.
 
-For example the [DOT language](https://en.wikipedia.org/wiki/DOT_(graph_description_language)) allows
+For example the [DOT language][dot-language] allows
 you to write a textual description of a graph which is then transformed into a picture by one of
-the [Graphviz](http://graphviz.org/) tools (such as `dot`). A simple graph looks like this:
+the [Graphviz][] tools (such as `dot`). A simple graph looks like this:
 
     graph {
         graph [bgcolor="yellow"]
@@ -30,4 +29,9 @@ to create graph data structures. However, unlike the DOT Language, our DSL will
 be an internal DSL for use only in our language.
 
 More information about the difference between internal and external DSLs can be
-found [here](https://martinfowler.com/bliki/DomainSpecificLanguage.html).
+found [here][fowler-dsl].
+
+[dsl]: https://en.wikipedia.org/wiki/Domain-specific_language
+[dot-language]: https://en.wikipedia.org/wiki/DOT_(graph_description_language)
+[Graphviz]: http://graphviz.org/
+[fowler-dsl]: https://martinfowler.com/bliki/DomainSpecificLanguage.html

exercises/food-chain/description.md

@@ -6,7 +6,7 @@ While you could copy/paste the lyrics,
 or read them from a file, this problem is much more
 interesting if you approach it algorithmically.
 
-This is a [cumulative song](http://en.wikipedia.org/wiki/Cumulative_song) of unknown origin.
+This is a [cumulative song][cumulative-song] of unknown origin.
 
 This is one of many common variants.
 
@@ -62,3 +62,5 @@ I don't know why she swallowed the fly. Perhaps she'll die.
 I know an old lady who swallowed a horse.
 She's dead, of course!
 ```
+
+[cumulative-song]: http://en.wikipedia.org/wiki/Cumulative_song

exercises/forth/description.md

@@ -2,7 +2,7 @@
 
 Implement an evaluator for a very simple subset of Forth.
 
-[Forth](https://en.wikipedia.org/wiki/Forth_%28programming_language%29)
+[Forth][]
 is a stack-based programming language. Implement a very basic evaluator
 for a small subset of Forth.
 
@@ -24,3 +24,5 @@ more letters, digits, symbols or punctuation that is not a number.
 enough.)
 
 Words are case-insensitive.
+
+[Forth]: https://en.wikipedia.org/wiki/Forth_%28programming_language%29

exercises/go-counting/description.md

@@ -31,6 +31,7 @@ To be more precise an empty intersection is part of a player's territory
 if all of its neighbors are either stones of that player or empty
 intersections that are part of that player's territory.
 
-For more information see
-[wikipedia](https://en.wikipedia.org/wiki/Go_%28game%29) or [Sensei's
-Library](http://senseis.xmp.net/).
+For more information see [wikipedia][go-wikipedia] or [Sensei's Library][go-sensei].
+
+[go-wikipedia]: https://en.wikipedia.org/wiki/Go_%28game%29
+[go-sensei]: http://senseis.xmp.net/

exercises/grep/description.md

@@ -3,7 +3,7 @@
 Search a file for lines matching a regular expression pattern. Return the line
 number and contents of each matching line.
 
-The Unix [`grep`](http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html) command can be used to search for lines in one or more files
+The Unix [`grep`][grep] command can be used to search for lines in one or more files
 that match a user-provided search query (known as the *pattern*).
 
 The `grep` command takes three arguments:
@@ -75,3 +75,5 @@ The `grep` command should support multiple flags at once.
 
 For example, running `grep -l -v "hello" file1.txt file2.txt` should
 print the names of files that do not contain the string "hello".
+
+[grep]: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html