Code

I found this puzzle in the internet. It looks quite easy to solve, but if you want to dig deeper into this you can find quite interesting fact.

Solution (without spoilers):
Let's name those rules with letters as follows:

A 206 twoNumbersAreCorrectButWrongPlaced

B 682 oneNumberIsCorrectAndWellPlaced 

C 614 oneNumberIsCorrectButWrongPlaced 

D 780 oneNumberIsCorrectButWrongPlaced 

E 738 nothingIsCorrect

How many codes is still in game after applying rules?

Count valid codes in case we are applying only two rules:

X	A	B	C	D	E
A	69	14	25	25	42
B	14	192	40	40	72
C	25	40	386	144	152
D	25	40	144	386	78
E	42	72	152	78	343

Now let's focus on AB and another rule:

ABA 14

ABB 14

ABC 1

ABD 7

ABE 10

So if the winner exists we can focus on rules ABC to find it.

If you want to figure out how to solve it in java you can find answer on github [WARNING: spoiler in tests]:

https://github.com/piotrpietrzak/codebreaker