combT =: ([: ; ([ ; [: i.@>: -~) ((1 {:: [) ,.&.> [: ,&.>/\. >:&.>@:])^:(0 {::
[) (<i.1 0),~ (< i.0 0) $~ -~)
a =. ". > cutLF wdclippaste ''
4 5 6 7 8 +/@:(150 = a +/@:{~"1 combT )"(0) 20
(itemized results that give solution to part2 as well.)
these versions do it without comb
a +/@:((150 = +/@:#~)"1) (20#2) #: i. 2^20
a +/@:(150 = +/"1@:(#~ ( #~ (9&> *. 3&<)@(+/"1)))) (20#2) #: i. 2^20
a +/@:(150 = +/"1@:(#~ ( #~ (4&=)@(+/"1)))) (20#2) #: i. 2^20
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