Double check the description and make improvements. Here's a recommended description:

Task
Write a function that takes an array of integers whose length is odd ( ≥ 3 ).
Every element in the array has the same value except for one unique element.
Return that unique element.

Guarantees
• The array length is odd.
• Exactly one element differs from the others.
• All values are integers.

Examples
[1, 1, 2] => 2
[17, 17, 3, 17, 17, 17, 17] => 3

Clarification
If the array is [4, 4, 4, 9, 4], the function should return 9, because 9 is the only value that is not equal to 4.

Haskell translation

Certain incorrect solutions can pass if you try the tests repeatedly (at least in Python - have not tested other languages).

The full definition of the TreeNode should be in preloaded, not in the user solution. This affects all languages except Python.

C++: No random tests

TypeScript translation (literal translation of JavaScript; author inactive)

Language: C++

Test suit missing the required header std::vector

Add some almost sorted fixed tests like [1, 3, 9, 4] to invalidate wrong solutions currently passing tests by chance.

Scala translation

Tests seem to be broken.
I keep getting expected [ undefined ] to deeply equal [ 1, 2, 3, 7, 16, 17 ] even though I am returning the array in the correct order

Go translation

D translation

Implement the methods anyMatch (any_match in PHP) & allMatch (all_match in PHP), which accepts a linked list (head) and a predicate function, and returns true if any / all of the elements apply to the given predicate.

This is hardly understandable, misleading and should be reworded. The predicate doesn't applicate to the elements of the list but to their respective .data field.