RosettaCodeData/Task/Longest-common-subsequence/J/longest-common-subsequence-1.j

lcs=: dyad define
 |.x{~ 0{"1 cullOne^:_ (\: +/"1)(\:{."1) 4$.$. x =/ y
)

cullOne=: ({~[: <@<@< [: (i. 0:)1,[: *./[: |: 2>/\]) :: ]