Add tasks for all the new languages

Task/Symmetric-difference/Apex/symmetric-difference.apex

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+Set<String> setA = new Set<String>{'John', 'Bob', 'Mary', 'Serena'};
+Set<String> setB = new Set<String>{'Jim', 'Mary', 'John', 'Bob'};
+
+// Option 1
+Set<String> notInSetA = setB.clone();
+notInSetA.removeAll(setA);
+
+Set<String> notInSetB = setA.clone();
+notInSetB.removeAll(setB);
+
+Set<String> symmetricDifference = new Set<String>();
+symmetricDifference.addAll(notInSetA);
+symmetricDifference.addAll(notInSetB);
+
+// Option 2
+Set<String> union = setA.clone();
+union.addAll(setB);
+
+Set<String> intersection = setA.clone();
+intersection.retainAll(setB);
+
+Set<String> symmetricDifference2 = union.clone();
+symmetricDifference2.removeAll(intersection);
+
+System.debug('Not in set A: ' + notInSetA);
+System.debug('Not in set B: ' + notInSetB);
+System.debug('Symmetric Difference: ' + symmetricDifference);
+System.debug('Symmetric Difference 2: ' + symmetricDifference2);

Task/Symmetric-difference/Lasso/symmetric-difference.lasso

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+[
+var(
+    'a'  = array(
+       'John'
+      ,'Bob'
+      ,'Mary'
+      ,'Serena'
+    )
+
+   ,'b'  = array
+
+);
+
+$b->insert( 'Jim' ); // Alternate method of populating array
+$b->insert( 'Mary' );
+$b->insert( 'John' );
+$b->insert( 'Bob' );
+
+$a->sort( true ); // arrays must be sorted (true = ascending) for difference to work
+$b->sort( true );
+
+$a->difference( $b )->union( $b->difference( $a ) );
+
+]

Task/Symmetric-difference/Nim/symmetric-difference.nim

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+import sets
+
+var setA = ["John", "Bob", "Mary", "Serena"].toSet
+var setB = ["Jim", "Mary", "John", "Bob"].toSet
+echo setA -+- setB # Symmetric difference
+echo setA - setB # Difference
+echo setB - setA # Difference

Task/Symmetric-difference/Ring/symmetric-difference.ring

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+alist = []
+blist = []
+alist = ["john", "bob", "mary", "serena"]
+blist = ["jim", "mary", "john", "bob"]
+
+alist2 = []
+for i = 1 to len(alist)
+    flag = 0
+    for j = 1 to len(blist)
+        if alist[i] = blist[j]  flag = 1 ok
+    next
+    if (flag = 0) add(alist2, alist[i]) ok
+next
+
+blist2 = []
+for j = 1 to len(alist)
+    flag = 0
+    for i = 1 to len(blist)
+        if alist[i] = blist[j]  flag = 1 ok
+    next
+    if (flag = 0) add(blist2, blist[j]) ok
+next
+see "a xor b :" see nl
+see alist2
+see blist2 see nl
+see "a-b :" see nl
+see alist2 see nl
+see "b-a :" see nl
+see blist2 see nl

Task/Symmetric-difference/Sidef/symmetric-difference.sidef

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+var a = ["John", "Serena", "Bob", "Mary", "Serena"];
+var b = ["Jim", "Mary", "John", "Jim", "Bob"];
+a ^ b -> unique.dump.say;

Task/Symmetric-difference/Swift/symmetric-difference.swift

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+let setA : Set<String> = ["John", "Bob", "Mary", "Serena"]
+let setB : Set<String> = ["Jim", "Mary", "John", "Bob"]
+println(setA.exclusiveOr(setB)) // symmetric difference of A and B
+println(setA.subtract(setB)) // elements in A that are not in B

Task/Symmetric-difference/jq/symmetric-difference-1.jq

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+# The following implementation of intersection (but not symmetric_difference) assumes that the
+# elements of a (and of b) are unique and do not include null:
+def intersection(a; b):
+  reduce ((a + b) | sort)[] as $i
+    ([null, []]; if .[0] == $i then [null, .[1] + [$i]] else [$i, .[1]] end)
+  | .[1] ;
+
+def symmetric_difference(a;b):
+  (a|unique) as $a | (b|unique) as $b
+  | (($a + $b) | unique) - (intersection($a;$b));

Task/Symmetric-difference/jq/symmetric-difference-2.jq

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+symmetric_difference( [1,2,1,2]; [2,3] )
+[1,3]