AoC day 22 (pt 1) dc

[q] sX

z 2/ d se sf                        # get deck sizes (assuming half of input each), set end ptrs
0 sp                                # set the start ptr (next card to be played)

# initialize arrays with input (S macro parameter to set array)
[
    li 1- dsi lSx
    li 0=X
    lIx
] sI

# S macros to parameterize the above I macro
[:a]sS le si lIx
[:b]sS lf si lIx

# Macro to calculate score (R macro parameter to read array)
[
    le 1- d lRx li * r se +     # top += read_array( --end_ptr ) * i
    le lp =X                    # check if (end == start)
    li 1+ si                    # inc i
    lVx                         # loop
] sV

# R macros to parameterize the above V macro
[ [;a]sR 1 si 0 lVx q ] sP
[ [;b]sR lf se 1 si 0 lVx q ] sQ    # parameterize the end_pointer by setting e = f

# Handle case where player 1 wins hand
[
    lp d;a le:a
    d;b le 1+:a 1+ sp
    le 2+ se
    s.0                             # replace the -1 on the stack with a 0
] sA

# Handle case where player 2 wins hand
[
    lp d;b lf:b
    d;a lf 1+:b 1+ sp
    lf 2+ sf
] sB

[
    _1                              # push -1 to signal when A macro doesn't run
    lp ddd le =Q lf =P              # check end of game, leaving two copies of ptr

    ;b r ;a >A                      # compare a(p) > b(p)
    _1 =B                           # if -1 left on stack, do else B macro

    lLx
] sL
lLx

[Part 1: ]np