Find the unique twins

Question

You will be given two Arrays / Lists / Vectors of non-negative integers A and B. Your task is to output the highest integer N that appears in both A and B, and is also unique in both A and B.

• You may assume that there is at least one such number.

• Any reasonable Input and Output method / format is allowed.

• These Loopholes are forbidden.

• This is code-golf, so the shortest code in every programming language wins!

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Test Cases:

A, B -> Output

[6], [1, 6] -> 6
[1, 2, 3, 4], [4, 5, 6, 7] -> 4
[0, 73, 38, 29], [38, 29, 73, 0] -> 73
[1, 3, 4, 6, 6, 9], [8, 7, 6, 3, 4, 3] -> 4
[2, 2, 2, 6, 3, 5, 8, 2], [8, 7, 5, 8] -> 5
[12, 19, 18, 289, 19, 17], [12, 19, 18, 17, 17, 289] -> 289
[17, 29, 39, 29, 29, 39, 18], [19, 19, 18, 20, 17, 18] -> 17
[17, 29, 39, 29, 29, 39, 18, 18], [19, 19, 18, 20, 17, 18] -> 17

Answer 1

Perl 5, 71 +2 (-ap) bytes

$F{$_}++for@F;map$\=$F{$_}^1||$L{$_}>1||$_<$\?$\:$_,keys%L;(%L,%F)=%F}{

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Answer 2

Java 8, 134 132 bytes

Both args are List<Integer>

a->b->a.stream().filter(i->b.stream().filter(j->i-j==0).count()*a.stream().filter(j->i-j==0).count()==1).max(Integer::compare).get()

Answer 3

Ruby, 56 49 bytes

->a,b{((r=a+b).select{|e|r.count(e)==2}&a&b).max}

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Answer 4

Axiom,126 74 68 58 bytes

q(a,b)==reduce(max,[x for x in a|count(x,a)*count(x,b)=1])

And with this I have less characters of JavaScript solutions and in general easier to read too (at last now...)

In mathematical words it would "find the max element of the list of the x in a, that are present 1 time only in a and 1 time only in b". This suppose that exist one element of the List [x for x in a|count(x,a)=1 and count(x,b)=1] as the question require. The other solution of 126 bytes

f(a,b)==(c:=reverse(sort(setIntersection(a,b)));for i in 1..#c repeat if count(c.i,a)=1 and count(c.i,b)=1 then return c.i;-1)

Results:

(6) -> q([1,2,3], [1,2,2,3])
   (6)  3
                                                    Type: PositiveInteger
(7) -> q([6], [1,6])
   (7)  6
                                                    Type: PositiveInteger
(8) -> q([1,2,3,4], [4,5,6,7])
   (8)  4
                                                    Type: PositiveInteger
(9) -> q([0,73,38,29], [38,29,73,0])
   (9)  73
                                                    Type: PositiveInteger
(10) -> q([1,3,4,6,6,9], [8,7,6,3,4,3])
   (10)  4
                                                    Type: PositiveInteger

Answer 5

PHP, 95 bytes

<?=max(array_intersect(e(A),e(B)));function e($a){return array_keys(array_count_values($a),1);}

Given A and B are defined constants holding each array.

Answer 6

APL NARS 40 28 chars

{⌈/g⍺∩(g←{⍵/⍨⊃1=+/(⊂⍵)=⍵})⍵}

g(⍵) return one list of elments of list ⍵ that appear in ⍵ 1 time only.

To the function for the question is assigned the name 'f' as (⍺)f(⍵) see below.

  f←{⌈/g⍺∩(g←{⍵/⍨⊃1=+/(⊂⍵)=⍵})⍵}
  1 2 3 f 1 2 2 3
3
  6 f 1 6
6
  1 2 3 4 f 4 5 6 7
4
  0 73 38 29 f 38 29 73 0
73
  1 3 4 6 6 9 f 8 7 6 3 4 3
4