RAT RUN: One Year Earlier

For the final preliminary 'free-roam' trial, the nine shortlisted rats were placed in a 9x9 space, and their movements were observed and recorded. Each of the digits 1-9 appeared in each row and column.

OBSERVATIONS:

• Every cell in the grid was visited, exactly once.
• No rat's path contained any repeated digits.
• No rat chose to move diagonally at any point.
• Every 2x2 area was visited by at least 2 rats.
• No two rats started on the same digit.
• No two rats ended on the same digit.
• All blackcurrants and redcurrants were eaten.
• No grapes were eaten.

BLACKCURRANTS: If a blackcurrant sits between two digits, one is double the other.

REDCURRANTS: If a redcurrant sits between two digits, one is odd and the other is even.

GRAPES: If a grape sits between two digits, they have a difference of at least 5.