AoC 2025, day 4 part 2 (dc)

# Command: tr '.@' '12' <input | dc -fdc-p2.dc

# line x y -> line x y
[
    _3R
    r dF0* 3R d3R+      # roll=150*y+x x y line
    d Sr 1 r:g          # push roll on r; grid(roll) = 1
    3R
] s@

[d] sd

0 Sr                    # Register stack r sentinel

2 ?                     # line y=2
[
    #[line: ]np
    0 r                 # line x=0 y
    [
        A~              # chr line x y
        2=@             # record @ (2); line x y
        r1+r            # line x++ y
        d0<X
    ] dsXx *+

    1+                  # y++
    ? z1<Y
] dsYx s.

[ ;g 3R+r ] s+

Lr                      # roll
[
    0r                  # roll count
    d F1+ l+x
    d F0+ l+x
    d E9+ l+x
    d  1+ l+x
    d  1- l+x
    d E9- l+x
    d F0- l+x
    d F1- l+x

    d3R d3R :n          # neigh(roll)=count; count roll

    4>d                 # dup roll if (count < 4)
    s.

    Lr d0<L
] dsLx +

[Part 1: ]n zps.

# count neigh roll -> count neigh roll neigh
[ rd _4Rr ] sP

[ d;n 1- d3=P r:n ] s-

[
    lp 1+ sp                # roll ...
    d F1+ l-x
    d F0+ l-x
    d E9+ l-x
    d  1+ l-x
    d  1- l-x
    d E9- l-x
    d F0- l-x
      F1- l-x

    z0<M
] dsMx

[Part 2: ]n lpp