Module day25

Code Chronicle

Efficiently checks if locks and keys overlap using bitwise logic. The ASCII character # (35) is odd and . (46) is even so bitwise AND with 1 results in either 1 or 0. The newline character \n (10) is even so will result in 0 and not contribute to matches. There are 25 bits plus 4 newline bits so each lock or key can be stored in an u32. For example:

   #####
   ##.##    11011
   .#.##    01011
   ...## => 00011 => 110110_010110_000110_000100_00010
   ...#.    00010
   ...#.    00010
   .....

Functions

• parse
• part1
• part2