i < res.size() so only initialized elements are accessed.

I doubt that banker's rounding is used for rounding prices. For example, the IRS rounding rule is to round half up. Most programming languages also use this rule for positive numbers (the only exceptions which I know are Python, R, .Net languages). So the expected rounding behavior should be clearly specified.

Approved

String.init len @@ const @@ Random.choice @@ Array.enum chars

Do not use const here. All generated words are in the form "AAAAAA" (one character repeated len times).

See my issue above. You should not modify the input to pass tests.

From the description: "Your function can modify the initial board value as much as you like, but the test suite will validate what you return, so don't forget to return it".

But if you modify rows of the initial board then you will not pass tests. Tests call the user solution with a shallow copy of board.

You skipped $5^1 + 5^2 + 5^3 = 155$ which is the 7th Chandos number.

[10, 3, 1, 0] is not a valid solution because it does not satisfy the condition d > 0.

Approved

You may replace the Bearing initialization line with

let a, b, c, d, e = Tuple5.of_enum (Enum.init 5 (fun id -> Bearing id))

to avoid warnings.

Haskell: The type of the initial solution should be Integer -> Int -> Integer.