Merge branch 'main' into update-tests-sgf-parsing

concepts/switch-statement/.meta/config.json

@@ -4,5 +4,6 @@
     "Azumix"
   ],
   "contributors": [
+    "josealonso"
   ]
 }

concepts/switch-statement/about.md

@@ -147,7 +147,23 @@ Starting with Java 14 (available as a preview before in Java 12 and 13) it is po
 
 You can find more information on enhanced switch [here][switch1], [here][switch2] and on the [oracle documentation][oracle-doc].
 
+In addition, a feature called `Guarded Patterns` was added in Java 21, which allows you to do checks in the case label itself.
+
+```java
+String dayOfMonth = getDayOfMonth();
+String day = "";
+return switch (day) {
+    case "Tuesday" when dayOfMonth == 13 -> "Forbidden day!!";
+    case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday" -> "Week day";
+    case "Saturday", "Sunday" -> "Weekend";
+    default -> "Unknown";
+};
+```
+
+You can find more information on the switch expression on Java 21 [here][switch-on-Java-21]
+
 [yield-keyword]: https://www.codejava.net/java-core/the-java-language/yield-keyword-in-java
 [switch1]: https://www.vojtechruzicka.com/java-enhanced-switch/
 [switch2]: https://howtodoinjava.com/java14/switch-expressions/
 [oracle-doc]: https://docs.oracle.com/en/java/javase/13/language/switch-expressions.html
+[switch-on-Java-21]: https://blog.adamgamboa.dev/switch-expression-on-java-21/#3-guarded-pattern

concepts/switch-statement/links.json

@@ -14,5 +14,9 @@
   {
     "url": "https://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html",
     "description": "oracle-doc"
+  },
+  {
+    "url": "https://blog.adamgamboa.dev/switch-expression-on-java-21/#3-guarded-pattern",
+    "description": "switch-on-Java-21"
   }
 ]

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

@@ -4,7 +4,7 @@ Create an implementation of the affine cipher, an ancient encryption system crea
 
 The affine cipher is a type of monoalphabetic substitution cipher.
 Each character is mapped to its numeric equivalent, encrypted with a mathematical function and then converted to the letter relating to its new numeric value.
-Although all monoalphabetic ciphers are weak, the affine cipher is much stronger than the atbash cipher, because it has many more keys.
+Although all monoalphabetic ciphers are weak, the affine cipher is much stronger than the Atbash cipher, because it has many more keys.
 
 [//]: # " monoalphabetic as spelled by Merriam-Webster, compare to polyalphabetic "
 

exercises/practice/anagram/.docs/instructions.append.md

@@ -0,0 +1,3 @@
+# Instructions Append
+
+The anagrams can be returned in any order.

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

@@ -1,6 +1,6 @@
 # Instructions
 
-Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
+Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.
 
 The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
 The first letter is replaced with the last letter, the second with the second-last, and so on.

exercises/practice/atbash-cipher/.meta/config.json

@@ -39,7 +39,7 @@
       "build.gradle"
     ]
   },
-  "blurb": "Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.",
+  "blurb": "Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.",
   "source": "Wikipedia",
   "source_url": "https://en.wikipedia.org/wiki/Atbash"
 }

exercises/practice/change/.docs/instructions.md

@@ -1,14 +1,8 @@
 # Instructions
 
-Correctly determine the fewest number of coins to be given to a customer such that the sum of the coins' value would equal the correct amount of change.
+Determine the fewest number of coins to give a customer so that the sum of their values equals the correct amount of change.
 
-## For example
+## Examples
 
-- An input of 15 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) or [5, 10]
-- An input of 40 with [1, 5, 10, 25, 100] should return one nickel (5) and one dime (10) and one quarter (25) or [5, 10, 25]
-
-## Edge cases
-
-- Does your algorithm work for any given set of coins?
-- Can you ask for negative change?
-- Can you ask for a change value smaller than the smallest coin value?
+- An amount of 15 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5 and one coin of value 10, or [5, 10].
+- An amount of 40 with available coin values [1, 5, 10, 25, 100] should return one coin of value 5, one coin of value 10, and one coin of value 25, or [5, 10, 25].

exercises/practice/change/.docs/introduction.md

@@ -0,0 +1,26 @@
+# Introduction
+
+In the mystical village of Coinholt, you stand behind the counter of your bakery, arranging a fresh batch of pastries.
+The door creaks open, and in walks Denara, a skilled merchant with a keen eye for quality goods.
+After a quick meal, she slides a shimmering coin across the counter, representing a value of 100 units.
+
+You smile, taking the coin, and glance at the total cost of the meal: 88 units.
+That means you need to return 12 units in change.
+
+Denara holds out her hand expectantly.
+"Just give me the fewest coins," she says with a smile.
+"My pouch is already full, and I don't want to risk losing them on the road."
+
+You know you have a few options.
+"We have Lumis (worth 10 units), Viras (worth 5 units), and Zenth (worth 2 units) available for change."
+
+You quickly calculate the possibilities in your head:
+
+- one Lumis (1 × 10 units) + one Zenth (1 × 2 units) = 2 coins total
+- two Viras (2 × 5 units) + one Zenth (1 × 2 units) = 3 coins total
+- six Zenth (6 × 2 units) = 6 coins total
+
+"The best choice is two coins: one Lumis and one Zenth," you say, handing her the change.
+
+Denara smiles, clearly impressed.
+"As always, you've got it right."

exercises/practice/collatz-conjecture/.docs/instructions.md

@@ -1,29 +1,3 @@
 # Instructions
 
-The Collatz Conjecture or 3x+1 problem can be summarized as follows:
-
-Take any positive integer n.
-If n is even, divide n by 2 to get n / 2.
-If n is odd, multiply n by 3 and add 1 to get 3n + 1.
-Repeat the process indefinitely.
-The conjecture states that no matter which number you start with, you will always reach 1 eventually.
-
-Given a number n, return the number of steps required to reach 1.
-
-## Examples
-
-Starting with n = 12, the steps would be as follows:
-
-0. 12
-1. 6
-2. 3
-3. 10
-4. 5
-5. 16
-6. 8
-7. 4
-8. 2
-9. 1
-
-Resulting in 9 steps.
-So for input n = 12, the return value would be 9.
+Given a positive integer, return the number of steps it takes to reach 1 according to the rules of the Collatz Conjecture.

exercises/practice/collatz-conjecture/.docs/introduction.md

@@ -0,0 +1,28 @@
+# Introduction
+
+One evening, you stumbled upon an old notebook filled with cryptic scribbles, as though someone had been obsessively chasing an idea.
+On one page, a single question stood out: **Can every number find its way to 1?**
+It was tied to something called the **Collatz Conjecture**, a puzzle that has baffled thinkers for decades.
+
+The rules were deceptively simple.
+Pick any positive integer.
+
+- If it's even, divide it by 2.
+- If it's odd, multiply it by 3 and add 1.
+
+Then, repeat these steps with the result, continuing indefinitely.
+
+Curious, you picked number 12 to test and began the journey:
+
+12 ➜ 6 ➜ 3 ➜ 10 ➜ 5 ➜ 16 ➜ 8 ➜ 4 ➜ 2 ➜ 1
+
+Counting from the second number (6), it took 9 steps to reach 1, and each time the rules repeated, the number kept changing.
+At first, the sequence seemed unpredictable — jumping up, down, and all over.
+Yet, the conjecture claims that no matter the starting number, we'll always end at 1.
+
+It was fascinating, but also puzzling.
+Why does this always seem to work?
+Could there be a number where the process breaks down, looping forever or escaping into infinity?
+The notebook suggested solving this could reveal something profound — and with it, fame, [fortune][collatz-prize], and a place in history awaits whoever could unlock its secrets.
+
+[collatz-prize]: https://mathprize.net/posts/collatz-conjecture/

exercises/practice/collatz-conjecture/.meta/config.json

@@ -35,6 +35,6 @@
     ]
   },
   "blurb": "Calculate the number of steps to reach 1 using the Collatz conjecture.",
-  "source": "An unsolved problem in mathematics named after mathematician Lothar Collatz",
-  "source_url": "https://en.wikipedia.org/wiki/3x_%2B_1_problem"
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Collatz_conjecture"
 }

exercises/practice/dominoes/.docs/instructions.md

@@ -2,7 +2,9 @@
 
 Make a chain of dominoes.
 
-Compute a way to order a given set of dominoes in such a way that they form a correct domino chain (the dots on one half of a stone match the dots on the neighboring half of an adjacent stone) and that dots on the halves of the stones which don't have a neighbor (the first and last stone) match each other.
+Compute a way to order a given set of domino stones so that they form a correct domino chain.
+In the chain, the dots on one half of a stone must match the dots on the neighboring half of an adjacent stone.
+Additionally, the dots on the halves of the stones without neighbors (the first and last stone) must match each other.
 
 For example given the stones `[2|1]`, `[2|3]` and `[1|3]` you should compute something
 like `[1|2] [2|3] [3|1]` or `[3|2] [2|1] [1|3]` or `[1|3] [3|2] [2|1]` etc, where the first and last numbers are the same.

exercises/practice/dominoes/.docs/introduction.md

@@ -0,0 +1,13 @@
+# Introduction
+
+In Toyland, the trains are always busy delivering treasures across the city, from shiny marbles to rare building blocks.
+The tracks they run on are made of colorful domino-shaped pieces, each marked with two numbers.
+For the trains to move, the dominoes must form a perfect chain where the numbers match.
+
+Today, an urgent delivery of rare toys is on hold.
+You've been handed a set of track pieces to inspect.
+If they can form a continuous chain, the train will be on its way, bringing smiles across Toyland.
+If not, the set will be discarded, and another will be tried.
+
+The toys are counting on you to solve this puzzle.
+Will the dominoes connect the tracks and send the train rolling, or will the set be left behind?

exercises/practice/eliuds-eggs/.docs/introduction.md

@@ -12,36 +12,54 @@ The position information encoding is calculated as follows:
 2. Convert the number from binary to decimal.
 3. Show the result on the display.
 
-Example 1:
+## Example 1
+
+![Seven individual nest boxes arranged in a row whose first, third, fourth and seventh nests each have a single egg.](https://assets.exercism.org/images/exercises/eliuds-eggs/example-1-coop.svg)
 
 ```text
-Chicken Coop:
  _ _ _ _ _ _ _
 |E| |E|E| | |E|
+```
+
+### Resulting Binary
+
+![1011001](https://assets.exercism.org/images/exercises/eliuds-eggs/example-1-binary.svg)
+
+```text
+ _ _ _ _ _ _ _
+|1|0|1|1|0|0|1|
+```
 
-Resulting Binary:
- 1 0 1 1 0 0 1
+### Decimal number on the display
 
-Decimal number on the display:
 89
 
-Actual eggs in the coop:
+### Actual eggs in the coop
+
 4
+
+## Example 2
+
+![Seven individual nest boxes arranged in a row where only the fourth nest has an egg.](https://assets.exercism.org/images/exercises/eliuds-eggs/example-2-coop.svg)
+
+```text
+ _ _ _ _ _ _ _
+| | | |E| | | |
 ```
 
-Example 2:
+### Resulting Binary
+
+![0001000](https://assets.exercism.org/images/exercises/eliuds-eggs/example-2-binary.svg)
 
 ```text
-Chicken Coop:
- _ _ _ _ _ _ _ _
-| | | |E| | | | |
+ _ _ _ _ _ _ _
+|0|0|0|1|0|0|0|
+```
 
-Resulting Binary:
- 0 0 0 1 0 0 0 0
+### Decimal number on the display
 
-Decimal number on the display:
 16
 
-Actual eggs in the coop:
+### Actual eggs in the coop
+
 1
-```

exercises/practice/flatten-array/.meta/config.json

@@ -6,6 +6,7 @@
     "aadityakulkarni",
     "FridaTveit",
     "jackattack24",
+    "jagdish-15",
     "jmrunkle",
     "jtigger",
     "kytrinyx",

exercises/practice/flatten-array/.meta/src/reference/java/Flattener.java

@@ -1,28 +1,17 @@
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 
-final class Flattener {
+class Flattener {
 
-    List flatten(final List nestedList) {
-        if (nestedList.isEmpty()) {
-            return new ArrayList<>();
-        } else {
-            final List result = new ArrayList();
-
-            final Object head = nestedList.get(0);
-            final List tail = nestedList.subList(1, nestedList.size());
-
-            if (head instanceof List) {
-                result.addAll(flatten((List) head));
-            } else {
-                result.add(head);
+    List<Object> flatten(List<?> list) {
+        List<Object> flattenedList = new ArrayList<>();
+        for (Object element: list) {
+            if (element instanceof List<?> listAsElement) {
+                flattenedList.addAll(flatten(listAsElement));
+            } else if (element != null) {
+                flattenedList.add(element);
             }
-
-            result.addAll(flatten(tail));
-            result.removeAll(Collections.singleton(null));
-            return result;
         }
+        return flattenedList;
     }
-
 }

exercises/practice/flatten-array/src/main/java/Flattener.java

@@ -2,7 +2,7 @@
 
 class Flattener {
 
-    <T> List<T> flatten(List<T> list) {
+    List<Object> flatten(List<?> list) {
         throw new UnsupportedOperationException("Delete this statement and write your own implementation.");
     }
 

exercises/practice/grade-school/.docs/instructions.md

@@ -1,21 +1,21 @@
 # Instructions
 
-Given students' names along with the grade that they are in, create a roster for the school.
+Given students' names along with the grade they are in, create a roster for the school.
 
 In the end, you should be able to:
 
-- Add a student's name to the roster for a grade
+- Add a student's name to the roster for a grade:
   - "Add Jim to grade 2."
   - "OK."
-- Get a list of all students enrolled in a grade
+- Get a list of all students enrolled in a grade:
   - "Which students are in grade 2?"
-  - "We've only got Jim just now."
+  - "We've only got Jim right now."
 - Get a sorted list of all students in all grades.
-  Grades should sort as 1, 2, 3, etc., and students within a grade should be sorted alphabetically by name.
-  - "Who all is enrolled in school right now?"
+  Grades should be sorted as 1, 2, 3, etc., and students within a grade should be sorted alphabetically by name.
+  - "Who is enrolled in school right now?"
   - "Let me think.
-    We have Anna, Barb, and Charlie in grade 1, Alex, Peter, and Zoe in grade 2 and Jim in grade 5.
-    So the answer is: Anna, Barb, Charlie, Alex, Peter, Zoe and Jim"
+    We have Anna, Barb, and Charlie in grade 1, Alex, Peter, and Zoe in grade 2, and Jim in grade 5.
+    So the answer is: Anna, Barb, Charlie, Alex, Peter, Zoe, and Jim."
 
-Note that all our students only have one name (It's a small town, what do you want?) and each student cannot be added more than once to a grade or the roster.
-In fact, when a test attempts to add the same student more than once, your implementation should indicate that this is incorrect.
+Note that all our students only have one name (it's a small town, what do you want?), and each student cannot be added more than once to a grade or the roster.
+If a test attempts to add the same student more than once, your implementation should indicate that this is incorrect.

exercises/practice/hamming/.docs/instructions.md

@@ -2,15 +2,6 @@
 
 Calculate the Hamming distance between two DNA strands.
 
-Your body is made up of cells that contain DNA.
-Those cells regularly wear out and need replacing, which they achieve by dividing into daughter cells.
-In fact, the average human body experiences about 10 quadrillion cell divisions in a lifetime!
-
-When cells divide, their DNA replicates too.
-Sometimes during this process mistakes happen and single pieces of DNA get encoded with the incorrect information.
-If we compare two strands of DNA and count the differences between them we can see how many mistakes occurred.
-This is known as the "Hamming distance".
-
 We read DNA using the letters C, A, G and T.
 Two strands might look like this:
 
@@ -20,8 +11,6 @@ Two strands might look like this:
 
 They have 7 differences, and therefore the Hamming distance is 7.
 
-The Hamming distance is useful for lots of things in science, not just biology, so it's a nice phrase to be familiar with :)
-
 ## Implementation notes
 
 The Hamming distance is only defined for sequences of equal length, so an attempt to calculate it between sequences of different lengths should not work.