March sync of practice exercise docs. (#3880)

Problem Spec Sync.

exercises/practice/affine-cipher/.docs/instructions.md

@@ -20,7 +20,7 @@ Where:
 
 - `i` is the letter's index from `0` to the length of the alphabet - 1.
 - `m` is the length of the alphabet.
-  For the Roman alphabet `m` is `26`.
+  For the Latin alphabet `m` is `26`.
 - `a` and `b` are integers which make up the encryption key.
 
 Values `a` and `m` must be _coprime_ (or, _relatively prime_) for automatic decryption to succeed, i.e., they have number `1` as their only common factor (more information can be found in the [Wikipedia article about coprime integers][coprime-integers]).

exercises/practice/flatten-array/.docs/instructions.md

@@ -1,11 +1,16 @@
 # Instructions
 
-Take a nested list and return a single flattened list with all values except nil/null.
+Take a nested array of any depth and return a fully flattened array.
 
-The challenge is to take an arbitrarily-deep nested list-like structure and produce a flattened structure without any nil/null values.
+Note that some language tracks may include null-like values in the input array, and the way these values are represented varies by track.
+Such values should be excluded from the flattened array.
 
-For example:
+Additionally, the input may be of a different data type and contain different types, depending on the track.
 
-input: [1,[2,3,null,4],[null],5]
+Check the test suite for details.
 
-output: [1,2,3,4,5]
+## Example
+
+input: `[1, [2, 6, null], [[null, [4]], 5]]`
+
+output: `[1, 2, 6, 4, 5]`

exercises/practice/flatten-array/.docs/introduction.md

@@ -0,0 +1,7 @@
+# Introduction
+
+A shipment of emergency supplies has arrived, but there's a problem.
+To protect from damage, the items — flashlights, first-aid kits, blankets — are packed inside boxes, and some of those boxes are nested several layers deep inside other boxes!
+
+To be prepared for an emergency, everything must be easily accessible in one box.
+Can you unpack all the supplies and place them into a single box, so they're ready when needed most?

exercises/practice/grains/.docs/instructions.md

@@ -1,15 +1,11 @@
 # Instructions
 
-Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
+Calculate the number of grains of wheat on a chessboard.
 
-There once was a wise servant who saved the life of a prince.
+A chessboard has 64 squares.
-The king promised to pay whatever the servant could dream up.
+Square 1 has one grain, square 2 has two grains, square 3 has four grains, and so on, doubling each time.
-Knowing that the king loved chess, the servant told the king he would like to have grains of wheat.
-One grain on the first square of a chess board, with the number of grains doubling on each successive square.
 
-There are 64 squares on a chessboard (where square 1 has one grain, square 2 has two grains, and so on).
+Write code that calculates:
 
-Write code that shows:
+- the number of grains on a given square
-
-- how many grains were on a given square, and
 - the total number of grains on the chessboard

exercises/practice/grains/.docs/introduction.md

@@ -0,0 +1,6 @@
+# Introduction
+
+There once was a wise servant who saved the life of a prince.
+The king promised to pay whatever the servant could dream up.
+Knowing that the king loved chess, the servant told the king he would like to have grains of wheat.
+One grain on the first square of a chessboard, with the number of grains doubling on each successive square.

exercises/practice/saddle-points/.docs/instructions.md

@@ -13,11 +13,12 @@ Or it might have one, or even several.
 Here is a grid that has exactly one candidate tree.
 
 ```text
+      ↓
       1  2  3  4
     |-----------
-1 | 9  8  7  8
+  1 | 9  8  7  8
-2 | 5  3  2  4  <--- potential tree house at row 2, column 1, for tree with height 5
+→ 2 |[5] 3  2  4
-3 | 6  6  7  1
+  3 | 6  6  7  1
 ```
 
 - Row 2 has values 5, 3, 2, and 4. The largest value is 5.

exercises/practice/sieve/.docs/instructions.md

@@ -6,37 +6,96 @@ A prime number is a number larger than 1 that is only divisible by 1 and itself.
 For example, 2, 3, 5, 7, 11, and 13 are prime numbers.
 By contrast, 6 is _not_ a prime number as it not only divisible by 1 and itself, but also by 2 and 3.
 
-To use the Sieve of Eratosthenes, you first create a list of all the numbers between 2 and your given number.
+To use the Sieve of Eratosthenes, first, write out all the numbers from 2 up to and including your given number.
-Then you repeat the following steps:
+Then, follow these steps:
 
-1. Find the next unmarked number in your list (skipping over marked numbers).
+1. Find the next unmarked number (skipping over marked numbers).
    This is a prime number.
 2. Mark all the multiples of that prime number as **not** prime.
 
-You keep repeating these steps until you've gone through every number in your list.
+Repeat the steps until you've gone through every number.
 At the end, all the unmarked numbers are prime.
 
 ~~~~exercism/note
-The tests don't check that you've implemented the algorithm, only that you've come up with the correct list of primes.
+The Sieve of Eratosthenes marks off multiples of each prime using addition (repeatedly adding the prime) or multiplication (directly computing its multiples), rather than checking each number for divisibility.
-To check you are implementing the Sieve correctly, a good first test is to check that you do not use division or remainder operations.
+
+The tests don't check that you've implemented the algorithm, only that you've come up with the correct primes.
 ~~~~
 
 ## Example
 
 Let's say you're finding the primes less than or equal to 10.
 
-- List out 2, 3, 4, 5, 6, 7, 8, 9, 10, leaving them all unmarked.
+- Write out 2, 3, 4, 5, 6, 7, 8, 9, 10, leaving them all unmarked.
+
+  ```text
+  2 3 4 5 6 7 8 9 10
+  ```
+
 - 2 is unmarked and is therefore a prime.
   Mark 4, 6, 8 and 10 as "not prime".
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] 9 [10]
+  ↑
+  ```
+
 - 3 is unmarked and is therefore a prime.
   Mark 6 and 9 as not prime _(marking 6 is optional - as it's already been marked)_.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+    ↑
+  ```
+
 - 4 is marked as "not prime", so we skip over it.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+       ↑
+  ```
+
 - 5 is unmarked and is therefore a prime.
   Mark 10 as not prime _(optional - as it's already been marked)_.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+          ↑
+  ```
+
 - 6 is marked as "not prime", so we skip over it.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+             ↑
+  ```
+
 - 7 is unmarked and is therefore a prime.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+                ↑
+  ```
+
 - 8 is marked as "not prime", so we skip over it.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+                   ↑
+  ```
+
 - 9 is marked as "not prime", so we skip over it.
+
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+                       ↑
+  ```
+
 - 10 is marked as "not prime", so we stop as there are no more numbers to check.
 
-You've examined all numbers and found 2, 3, 5, and 7 are still unmarked, which means they're the primes less than or equal to 10.
+  ```text
+  2 3 [4] 5 [6] 7 [8] [9] [10]
+                           ↑
+  ```
+
+You've examined all the numbers and found that 2, 3, 5, and 7 are still unmarked, meaning they're the primes less than or equal to 10.

exercises/practice/simple-cipher/.docs/instructions.md

@@ -11,14 +11,14 @@ If anyone wishes to decipher these, and get at their meaning, he must substitute
 Ciphers are very straight-forward algorithms that allow us to render text less readable while still allowing easy deciphering.
 They are vulnerable to many forms of cryptanalysis, but Caesar was lucky that his enemies were not cryptanalysts.
 
-The Caesar Cipher was used for some messages from Julius Caesar that were sent afield.
+The Caesar cipher was used for some messages from Julius Caesar that were sent afield.
 Now Caesar knew that the cipher wasn't very good, but he had one ally in that respect: almost nobody could read well.
 So even being a couple letters off was sufficient so that people couldn't recognize the few words that they did know.
 
-Your task is to create a simple shift cipher like the Caesar Cipher.
+Your task is to create a simple shift cipher like the Caesar cipher.
-This image is a great example of the Caesar Cipher:
+This image is a great example of the Caesar cipher:
 
-![Caesar Cipher][img-caesar-cipher]
+![Caesar cipher][img-caesar-cipher]
 
 For example:
 
@@ -44,7 +44,7 @@ would return the obscured "ldpdsdqgdehdu"
 In the example above, we've set a = 0 for the key value.
 So when the plaintext is added to the key, we end up with the same message coming out.
 So "aaaa" is not an ideal key.
-But if we set the key to "dddd", we would get the same thing as the Caesar Cipher.
+But if we set the key to "dddd", we would get the same thing as the Caesar cipher.
 
 ## Step 3