Doesn't it say a lot that the author himself gave a wrong solution to the 4th problem at first? Does he think he's a failed Software Engineer? (I wouldn't) ...

Doesn't it say a lot that the author himself gave a wrong solution to the 4th problem at first? Does he think he's a failed Software Engineer? (I wouldn't) ... because he does say on the 5th problem's solutions that he wouldn't consider anyone that wouldn't find a correct solution to those exercises.