day3-1.prdc

l{","/µ(17:)‡{|3%(}y\I°~}Ás}d&LwŠmŒ .. 35 bytes

{
l .. two lines please
{ .. process twice:
  ","/ .. divide into comma-separated tokens
  µ .. map across each token:
    ( .. uncons to get a U/D/L/R letter
    17:)‡   .. [17,18]
    {    .. we'll do this with both elements against the U/D/L/R ascii:
      |  .. binary or
      3% .. mod 3
      (  .. subtract 1
    }y .. through brute force, this formula was found to produce a displacement vector
    \I .. swap, convert to integer (this is the number after U/D/L/R)
    °  .. replicate
    ~  .. and expand onto the stack (so we're kind of flatmapping)
  }  .. done mapping
  Ás .. scan with vectorizing addition; this is the list of points visited by the wire
}d .. do this twice, to get the two wire paths
& .. intersect them
Lw .. take the absolute value of everything
Šm .. map with summing, to compute manhattan distances
Π.. minimum
};