Domino test case clarification of chain about rust HOT 5 CLOSED

A domino has two numbers physically etched onto the same stone. This image would correspond to (3, 4):

Individual domino stones are immutable; the same pair of numbers is always present on each stone, though you can of course place the stone in either orientation.

Your proposed solution is not possible with physical domino stones and is disallowed in the test cases.

from rust.

you cannot make a chain out of this set of dominoes, therefore dominoes::chain(vec![(1, 2), (4, 1), (2, 3)]) returns None instead of Some(chain) where chain is some valid chain

In the context of https://github.com/exercism/xrust/blob/master/exercises/dominoes/tests/dominoes.rs#L24 , Correct simply means that the provided dominoes::chain function returns a chain that:

• has the same number of dominoes as the input
• has the same dominoes as the input
• satisfies the chaining property that for any two adjacent dominoes (a, b), (c, d) that b == c, which also applies for the last domino and the first domino

41 12 23 is not a valid chain for the input (1, 2), (4, 1), (2, 3) because 4 != 3

from rust.

This was a challenging exercise!
Thanks!

from rust.

I don't understand why the following aren't valid, i.e. the corresponding tests expect None:
Input: [(1, 1), (2, 2)], Output: [(1, 2), (2, 1)]
Input: [(1, 2), (2, 1), (3, 4), (4, 3)], Output: [(3, 4), (4, 2), (2, 1), (1, 3)]

Every property mentioned in this comment is satisfied.

from rust.

Got it! In other words, the dominoes in the output [(1, 2), (2, 1)] aren't present in the input. Thanks.

from rust.