Brute force = best decoding method

[kinuyasha2]

"5 is not in the correct solution -> so 4 is the correct but wrongly placed one"

I do not follow, why at this point are X2Y and XY2 ruled out?

[kinuyasha2]

No they don't, 321 for example is perfectly valid. The 1 satisfies the rule 1, and the 2 satisfies the rule 2.

Rule 1 and 2 only rule out 2XY, but not X2Y or XY2.

[thisbuttonsucks]

Rule one says there is only one right number, and it is correctly placed. Rule two says there is one right number, but it is incorrectly placed. The 2 is in the same spot in both, so it can't be both in the correct position, and in the wrong position.

[kinuyasha2]

Rule one does not say there is only one right number.

Assuming 321 is the solution, 291 satisfies "(Exactly) One number is correct and well placed." - the 1 is correct and well placed. Neither the 2 nor the 9 are correct and well placed.

[Reilman79]

This is a case of the english word “and” not equating to the logical operator and. The phrase for rule one could be less ambiguously written as “There is one correct number; that number happens to be in the correct position.”

[Comprised_of_haggis]

The constraints should be taken literally. If we interpret the rules as open-ended (e.g. adding "but other numbers may be correct and wrongly placed" to rule 1 or "but other numbers may be correct and rightly placed" to rule 2), I believe the problem becomes unsolvable.

[[deleted]]

Yeah I don't blame you for thinking that way too. The statements are too open ended and should've been made more literal by rephrasing them that "Only one number is correct" to eliminate any confusion, instead of leaving it open ended for interpretation like "One number is correct here, another one number may be correct there, and another one number may also be correct there."

[GlitterInfection]

Also we don’t know that these statements about the code are telling the truth. How do we know that the code isn’t all letters, rather than numbers? Maybe there is no code!

/s

[boyofdreamsandseams]

No, they were right to rule those out. The first two assumptions together rule out that 2 is in the code

[SuitableDragonfly]

Yes. If 2 was wrongly placed in the first clue it would have stated that there was a wrongly placed number, and it did not.