Module aoc::year2022::day04

Camp Cleanup

This puzzle asks to compute range intersections. To simplify the 2nd part, we can use a trick. Rather than consider each possible case of intersection (overlapping start, overlapping end, completely enclosed or completely enclosing) it’s simpler to check if two ranges don’t overlap then invert.

If a and b are the ordered start and end of the first range and c and d the ordered start and end of the second range, then if:

a > d || c > b

the 2 ranges can’t overlap. Using DeMorgan’s laws this can be inverted to:

a <= d && c <= b

to check when two ranges do overlap.

Functions

• parse
  Parse each line into 4 integers.
• part1
  Count ranges completely enclosed by each other.
• part2
  Count ranges with any intersection.

Type Aliases

• Pairs 🔒