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

lcstr=:4 :0
  C=. ({.~ 1+$) x=/y
  M=. >./ (* * * >. * + (_1&|.)@:|:^:2)^:_  C
  N=. >./ M
  y {~ (M i. N)-i.-N
)