Kola nut
Macadamia
Mamoncillo
Maya nut
Mongongo
Oak acorns
Ogbono nut
Paradise nut
Pili nut
Pistachio
Walnut

["walnut", "walnut", "pistachio"]

["walnut", "pistachio", "walnut"]

~.`{`{=}+%1-,}+$.,)2//zip[]*.2<..&=*p

> ["walnut" "walnut" "walnut" "macadamia" "pistachio"]
["walnut" "macadamia" "walnut" "pistachio" "walnut"]

> ["walnut" "walnut" "walnut" "macadamia" "walnut"]
[]

~:x{]x-,}$.,)2//zip[]*.2<..&=*`

]`_:@.(0<2&([:+/=/))({.~-:@#),((],.|.)~>.@-:@#)<"1;(:#&.>)(</.])[;.1' ',1!:1[1

macadamia walnut walnut pistachio walnut

macadamia walnut walnut walnut pistachio

walnut walnut walnut macadamia pistachio

walnut macadamia walnut pistachio walnut

p.¬{s₂=}∨Ė

p.¬{s₂=}∨Ė
p            Find a permutation of {the input}
  ¬{   }     which does not have the following property:
    s₂         it contains a pair of adjacent elements
      =        that are equal
        ∨    {no constraint on what value the equal elements can have}
 .           If you find such a permutation, output it.
        ∨    If no permutation is found, ignore the input and
         Ė     {output} an empty list