nice

thank you for this. I didn't realize that even a range was an object. I know, I know, "everything" in Ruby is, but I'm still coming to terms with that. :)

This is a strange one, because the acceptance tests do not test for this.

If you also want to capitalize the last word add this code to the end: .sub(/(\w+)$/,&:capitalize)

substring_test "iNG", "NG"
=> false

should be
=> true

initials('Barack hussein obama')
=> "B.H.obama"

should be "B.H.Obama"

while told in the description, punctuation is never tested.

ruby random tests are TOTALLY wrong (retained letters are not the same than the one in the description and there may even be some letters that are filtered only from time to time... x( )

Something wrong with Ruby random test cases.
In Description: (To be clear, the acceptable characters for the plumage are 8,W,T,Y,U,I,O,A,H,X,V and M.)

Random Tests, Handles a few test cases:
Expected: "HETIHVCZPLIVLWDNDXLMTK8ULIBWYXYYJRIHM8FPTHZIYKATTVVAUOVWWQVJHZVWOQXHS8IRYUZXWMSOYPWJBCTANRUJYHDATFQTRVUNHHDQMFINJZWMICRL''0v0''LRCIMWZJNIFMQDHHNUVRTQFTADHYJURNATCBJWPYOSMWXZUYRI8SHXQOWVZHJVQWWVOUAVVTTAKYIZHTPF8MHIRJYYXYWBILU8KTMLXDNDWLVILPZCVHITEH", instead got: "HTIHVIVWXMT8UIWYXYYIHM8THIYATTVVAUOVWWVHVWOXH8IYUXWMOYWTAUYHATTVUHHMIWMI''0v0''IMWIMHHUVTTAHYUATWYOMWXUYI8HXOWVHVWWVOUAVVTTAYIHT8MHIYYXYWIU8TMXWVIVHITH"

From description: "You need to design a recursive function...."

dropzone([5, 2], [[8, 0], [5, 4], [5, 0]])
Expected: [5, 0], instead got: [5, 4].

Typo in "Find exapmles below:"

table_game [[1,2,1], [1,2,1], [98,99,1]]
=> [1, 1, 98, 1]

wrong

Maybe add a test for [1,1,-1,-1, ... random !=0 ...] (Ruby)?
Several solutions should fail.

arr = [2, 2, -2, -2]
=> [2, 2, -2, -2]
closest arr
=> 2
"Return None if it is not possible to define only one of such values."

arr = [-1, 1]
=> [-1, 1]
explode arr
=> "Void!"

arr = ['-1', 1]
=> ["-1", 1]
explode arr
=> "Void!"

:)