smalltalk: eight-queens classic program (sizes 1/4/5 verified)

lib/smalltalk/tests/programs.sx

@@ -82,4 +82,64 @@
      ^ b memoFib: 10")
   55)
 
+;; ── eight-queens.st (kept in sync with lib/smalltalk/tests/programs/eight-queens.st) ──
+(define
+  queens-source
+  "Object subclass: #EightQueens
+     instanceVariableNames: 'columns count size'!
+
+   !EightQueens methodsFor: 'init'!
+   init
+     size := 8.
+     columns := Array new: size.
+     count := 0.
+     ^ self!
+
+   size: n
+     size := n.
+     columns := Array new: n.
+     count := 0.
+     ^ self! !
+
+   !EightQueens methodsFor: 'access'!
+   count ^ count!
+
+   size ^ size! !
+
+   !EightQueens methodsFor: 'solve'!
+   solve
+     self placeRow: 1.
+     ^ count!
+
+   placeRow: row
+     row > size ifTrue: [count := count + 1. ^ self].
+     1 to: size do: [:col |
+       (self isSafe: col atRow: row) ifTrue: [
+         columns at: row put: col.
+         self placeRow: row + 1]]!
+
+   isSafe: col atRow: row
+     | r prevCol delta |
+     r := 1.
+     [r < row] whileTrue: [
+       prevCol := columns at: r.
+       prevCol = col ifTrue: [^ false].
+       delta := col - prevCol.
+       delta abs = (row - r) ifTrue: [^ false].
+       r := r + 1].
+     ^ true! !")
+
+(smalltalk-load queens-source)
+
+;; Backtracking is correct but slow on the spec interpreter (call/cc per
+;; method, dict-based ivar reads). 4- and 5-queens cover the corners
+;; and run in under 10s; 6+ work but would push past the test-runner
+;; timeout. The class itself defaults to size 8, ready for the JIT.
+(st-test "1 queen on 1x1 board" (evp "^ (EightQueens new size: 1) solve") 1)
+(st-test "4 queens on 4x4 board" (evp "^ (EightQueens new size: 4) solve") 2)
+(st-test "5 queens on 5x5 board" (evp "^ (EightQueens new size: 5) solve") 10)
+(st-test "EightQueens class is registered" (st-class-exists? "EightQueens") true)
+(st-test "EightQueens init sets size 8"
+  (evp "^ EightQueens new init size") 8)
+
 (list st-test-pass st-test-fail)

lib/smalltalk/tests/programs/eight-queens.st

@@ -0,0 +1,47 @@
+"Eight-queens — classic backtracking search. Counts the number of
+ distinct placements of 8 queens on an 8x8 board with no two attacking.
+ Expected count: 92."
+
+Object subclass: #EightQueens
+  instanceVariableNames: 'columns count size'!
+
+!EightQueens methodsFor: 'init'!
+init
+  size := 8.
+  columns := Array new: size.
+  count := 0.
+  ^ self!
+
+size: n
+  size := n.
+  columns := Array new: n.
+  count := 0.
+  ^ self! !
+
+!EightQueens methodsFor: 'access'!
+count ^ count!
+
+size ^ size! !
+
+!EightQueens methodsFor: 'solve'!
+solve
+  self placeRow: 1.
+  ^ count!
+
+placeRow: row
+  row > size ifTrue: [count := count + 1. ^ self].
+  1 to: size do: [:col |
+    (self isSafe: col atRow: row) ifTrue: [
+      columns at: row put: col.
+      self placeRow: row + 1]]!
+
+isSafe: col atRow: row
+  | r prevCol delta |
+  r := 1.
+  [r < row] whileTrue: [
+    prevCol := columns at: r.
+    prevCol = col ifTrue: [^ false].
+    delta := col - prevCol.
+    delta abs = (row - r) ifTrue: [^ false].
+    r := r + 1].
+  ^ true! !