AoC 2025, day 1, part 2 (dc)

# Command: tr 'LR' '_ ' <input | dc -fdc-p2.dc

0                   # count
[0*]sZ

50
?                   # move pos count
[
    A0~             # move%100 move/100 pos count

    r d*v 4R+_3R    # count += abs(move/100)

    rd3R +          # pos+=move oldpos count

    d1r 0<Z r       # pos (pos<=0) oldpos count
    d1r A0>Z 3R+    # (pos>=100)+(pos<=0) pos oldpos count
    3R 0=Z          # 0 if oldpos was 0 (avoid double count)
    3R+ r           # count += bool result

    A0 d3R +r%      # newpos = (pos + 100) % 100  (+100 needed for positive residue)
    ? z2<M
] dsMx

[Part 2: ]nrp