AoC 2024, day 5, part 1 (dc)

# Command: tr -cs '[0-9\n]' ' ' <input | dc -fdc-p1.dc

[ lp ln2/1+;l+ sp ] sP

# Read in rules section
?
[
    rA0*+ 1 r:r
    ? z0<L
] dsLx

# Process
?
[
    # Load list
    z dsn                   # n = size of list, stack: i=0 ln ln-1 ... l1
    [
        d_3R :l             # set list(i)
        1- d0<I
    ] dsIx                  # end: 0 on stack

    # Check list
    ln                      # i = n, stack: i sum=0
    [
        d1-                 # j = n-1, stack: j i sum
        [
            d3Rd            # i i j j sum
            ;l3R;l          # list(j) list(i) i j sum
            A0*+;r          # rule(j|i) i j sum
            4R+_3R          # add rule to sum
            r1- d0<J        # j--
        ] dsJx +            # end: stack: i+0 sum

        1- d1<I             # i--
    ] dsIx *                # end: stack: sum*1

    ln d1-*2/               # triangle( n-1 )
    =P                      # P if triangle == sum

    ? z0<L
] dsLx

[Part 1: ]n lpp