Question 15
A robot can generate a set of digit codes according to user’s reasonable instructions. Wayne gives out the following commands:
(1) Each code is a four-digit number (nonzero for the left-most digit).
(2) Every two codes in the set have identical digits at no more than two corresponding positions.
Find the maximum number of codes in a set the robot can generate.
(1) Each code is a four-digit number (nonzero for the left-most digit).
(2) Every two codes in the set have identical digits at no more than two corresponding positions.
Find the maximum number of codes in a set the robot can generate.