lambdaway :: intersection

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_h1 intersection

_p Following [[http://rosettacode.org/wiki/Common_list_elements|http://rosettacode.org/wiki/Common_list_elements]]

{prewrap
'{intersection 
 {A.new 3 5 6 2 9 8 4} 
 {A.new 2 5 1 3 8 9 4 6}
 {A.new 1 3 7 6 9} 
} 
-> {intersection 
 {A.new 3 5 6 2 9 8 4} 
 {A.new 2 5 1 3 8 9 4 6}
 {A.new 1 3 7 6 9}
}

A  isinB isinC []
2  yes   no    []
5  no    no    []
1  no    no    []
3  yes   yes   [3]
8  yes   no    [3]
9  yes   yes   [3,9]
4  yes   no    [3,9]
6  yes   yes   [3,9,6]

'{def intersection
 
 {def intersection.r
  {lambda {:a :b :c :d}
   {if {A.empty? :a}
    then :d
    else {intersection.r {A.rest :a} :b :c
             {if {and {> {A.in? {A.first :a} :b} -1}
                      {> {A.in? {A.first :a} :c} -1}}
              then {A.addlast! {A.first :a} :d}
              else :d} }}}}

{lambda {:a :b :c}
  {A.sort! < {intersection.r :a :b :c {A.new}}} }}
-> {def intersection
 
 {def intersection.r
  {lambda {:a :b :c :d}
   {if {A.empty? :a}
    then :d
    else {intersection.r {A.rest :a} :b :c
             {if {and {> {A.in? {A.first :a} :b} -1}
                      {> {A.in? {A.first :a} :c} -1}}
              then {A.addlast! {A.first :a} :d}
              else :d} }}}}

{lambda {:a :b :c}
  {A.sort! < {intersection.r :a :b :c {A.new}}} }}
}

_p Doesn't depend on input lists order, but better if it is in increasing length.

lambdaway v.20211111