June 2018 Update

Task/Permutations/Smalltalk/permutations-2.st

@@ -0,0 +1,27 @@
+ArrayedCollection extend [
+
+    permuteAndDo: aBlock
+        ["Permute receiver in-place, and call aBlock.
+        Requires integer keys."
+        self permuteUpto: self size andDo: aBlock]
+
+    permuteUpto: n andDo: aBlock
+        [n = 0 ifTrue: [^aBlock value].
+        1 to: n do:
+            [:i |
+            self swap: i with: n.
+            self permuteUpto: n-1 andDo: aBlock.
+            self swap: i with: n]]
+]
+
+SequenceableCollection extend [
+
+    permutations
+        ["Answer a ReadStream of permuted shallow copies of receiver."
+        | c |
+        c := MappedCollection
+            collection: self
+            map: self keys asArray.
+        ^Generator on:
+            [:g |
+            c map permuteAndDo: [g yield: (c copyFrom: 1 to: c size)]]]

Task/Permutations/Smalltalk/permutations-3.st

@@ -0,0 +1,2 @@
+st> 'Abc' permutations contents
+('bcA' 'cbA' 'cAb' 'Acb' 'bAc' 'Abc' )