feat: kata/average-of-even-numbers-in-a-list (#856)

* docs: kata description

* feat: kata/average-of-even-numbers-in-a-list

---------

Co-authored-by: ParanoidUser <[email protected]>

Author: github-actions[bot]

kata/beta/average-of-even-numbers-in-a-list/README.md

@@ -0,0 +1,41 @@
+# [Average of Even Numbers in a List](https://www.codewars.com/kata/average-of-even-numbers-in-a-list "https://www.codewars.com/kata/685a10c62388b0a0220ac88d")
+
+Your task is to write a method that calculates the average of all even numbers in a list of integers.
+If the list contains no even numbers, return `0.0`.
+
+---
+
+## Function Signature
+
+```java
+public static double averageOfEvens(List<Integer> numbers)
+```
+
+---
+
+## Input
+
+A `List<Integer>` of length n (1 ≤ n ≤ 100,000)
+
+---
+
+## Output
+
+A `double` representing the average of all even numbers in the list.
+If there are no even numbers, return `0.0`
+
+---
+
+## Examples
+
+```java
+averageOfEvens(Arrays.asList(2, 4,6,8,10))=>6.0
+
+averageOfEvens(Arrays.asList(1, 3,5))=>0.0
+
+averageOfEvens(Arrays.asList(10, 15,20,25,30))=>20.0
+
+averageOfEvens(Arrays.asList(0, 0,0))=>0.0
+
+averageOfEvens(Arrays.asList(1, -4,-6,3))=>-5.0
+```

kata/beta/average-of-even-numbers-in-a-list/main/EvenAverage.java

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+import java.util.List;
+
+interface EvenAverage {
+  static double averageOfEvens(List<Integer> numbers) {
+    return numbers.stream().mapToInt(i -> i).filter(i -> i % 2 == 0).average().orElse(0);
+  }
+}

kata/beta/average-of-even-numbers-in-a-list/test/SolutionTest.java

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+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+  @Test
+  void sample() {
+    assertEquals(6.0, EvenAverage.averageOfEvens(List.of(2, 4, 6, 8, 10)));
+    assertEquals(0.0, EvenAverage.averageOfEvens(List.of(1, 3, 5)));
+    assertEquals(20.0, EvenAverage.averageOfEvens(List.of(10, 15, 20, 25, 30)));
+    assertEquals(0.0, EvenAverage.averageOfEvens(List.of(0, 0, 0)));
+    assertEquals(-5.0, EvenAverage.averageOfEvens(List.of(1, -4, -6, 3)));
+  }
+}

kata/beta/index.md

@@ -1,5 +1,6 @@
 - [02. Sum of array's elements](02-sum-of-arrays-elements "58f475735e78fde4a2000011")
 - [¡Arrest the cardiac!](arrest-the-cardiac "660af4c7fe0da42cceb4af56")
+- [Average of Even Numbers in a List](average-of-even-numbers-in-a-list "685a10c62388b0a0220ac88d")
 - [Bad Collection?](bad-collection "5e36fb0ffc5a260001e65a5b")
 - [Basic Arabic-To-Roman Numerals (1 to 999)](basic-arabic-to-roman-numerals-1-to-999 "5580d8dc8e4ee9ffcb000050")
 - [Beginner friendly: remove the letter o](beginner-friendly-remove-the-letter-o "58d3dd53b0fe8c9ac10000b3")