smalltalk: quicksort classic program + 9 tests

lib/smalltalk/tests/programs/quicksort.st

@@ -0,0 +1,31 @@
+"Quicksort — Lomuto partition. Sorts an Array in place. Classic-corpus
+ program for the Smalltalk-on-SX runtime."
+
+Object subclass: #Quicksort
+  instanceVariableNames: ''!
+
+!Quicksort methodsFor: 'sort'!
+sort: arr ^ self sort: arr from: 1 to: arr size!
+
+sort: arr from: low to: high
+  | p |
+  low < high ifTrue: [
+    p := self partition: arr from: low to: high.
+    self sort: arr from: low to: p - 1.
+    self sort: arr from: p + 1 to: high].
+  ^ arr!
+
+partition: arr from: low to: high
+  | pivot i tmp |
+  pivot := arr at: high.
+  i := low - 1.
+  low to: high - 1 do: [:j |
+    (arr at: j) <= pivot ifTrue: [
+      i := i + 1.
+      tmp := arr at: i.
+      arr at: i put: (arr at: j).
+      arr at: j put: tmp]].
+  tmp := arr at: i + 1.
+  arr at: i + 1 put: (arr at: high).
+  arr at: high put: tmp.
+  ^ i + 1! !