AoC 2024, day 9, part 1 (dc)

# Command: dc -fdc-p1.dc <input

# Unpack input onto stack
?
[
    10~r
    d0<L
] dsLx +

[digits unpacked: ]nzps.
dsl1                                # left = start (size of file #0); stack: file idx next ...
[
    r3R +                           # idx += next (gap); idx file nextNext ...
    3R                              # i=next idx file ...
    [
        rd 4Rd 3R:d                 # disk(idx)=file; file idx i
        r1+                         # idx++ file i
        3R 1- d0<I                  # i--; loop
    ] dsIx +                        # idx file

    r1+                             # file++ idx next rest
    z2<L
] dsLx s.

ll1-                                # stack: left right
[
    rdd;d r0r:d                     # disk(right) right left; disk(right) = 0
    3R d3R r:d                      # disk(left) = disk(right); stack: left right

    [
        1+ d;d 0!=L                 # inc left until not zero
    ] dsLx

    r
    [
        1- d;d 0=R                  # dec right until zero
    ] dsRx

    d3Rd3R >M                       # loop while (right > left); left right
] dsMx

0r                                  # i sum=0
[
    dd;d * 3R+                      # sum += disk(i) * i
    r1- d0<L
] dsLx +

[Part 1: ]np