load 'aoc.ijs'
d =: nums 'day01'

*/ {: (#"1~ 2020&=@:(+/)) |:,/,"0/~ d                       NB. 805731
([ * 2020 - [) (<./ (i. (2020&-)) d) { d                    NB. bit faster
*/2{.d/:(2020-d)i.d                                         NB. shortest

*/ {:"1 (#"1~ 2020&=@:(+/)) |: d {~ ((#: i.@(*/)) 3 ## d)   NB. 192684960