day3-1.prdc

l¬μ"\d+"El¨Im»~\u+ßd*¨}¨$G«_# .. 29 bytes

{
l¬ .. get lines
μ  .. for each line:
  "\d+"El .. regex match runs of digits
  ¨   .. flatten, since every list is length-1 with the entire match
  Im  .. convert to integers
  »   .. drop head (we don't need the first number for day 1)
      .. We now have a list [a, b, c, d]
      .. and we need to get [a, a+c) * [b, b+d).
  ~   .. expand onto the stack
  \u  .. swap underneath to get a, c, b, d
  +ßd .. black magic... ok let's break it down: + is addition.
      ..
      .. ß modifies addition to get "bindmap": take the second value on
      .. the stack and add it to every value in the first. Since the top
      .. value on the stack is an integer and not a .. list, it is
      .. coerced to the half-open range.
      ..
      .. d modifies +ß to perform it twice. After running it once and
      .. seeing b, d popped and converted to the newly pushed list
      .. [b, b+d), it temporarily holds that list elsewhere and runs
      .. +ß again on the values beneath, which are a, c.
      ..
 *    .. Take that cartesian product
 ¨    .. flatten once
}
¨     .. flatten
$G    .. Sort and group, as always
«_#   .. Count groups that are > 1 length
      .. This works because « takes the all-but-last slice of the list;
      .. that slice is empty, and therefore falsy, iff the group is
      .. length ≤ 1.
};