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Task/Paraffins/Racket/paraffins.rkt

@@ -0,0 +1,36 @@
+#lang racket
+
+(define MAX_N 33)
+(define BRANCH 4)
+
+(define rooted   (make-vector MAX_N 0))
+(define unrooted (make-vector MAX_N 0))
+(for ([i 2]) (vector-set! rooted i 1) (vector-set! unrooted i 1))
+
+(define (vector-inc! v i d) (vector-set! v i (+ d (vector-ref v i))))
+
+(define (choose m k)
+  (if (= k 1) m
+      (for/fold ([r m]) ([i (in-range 1 k)]) (/ (* r (+ m i)) (add1 i)))))
+
+(define (tree br n cnt sum l)
+  (let/ec return
+    (for ([b (in-range (add1 br) (add1 BRANCH))])
+      (define s (+ sum (* (- b br) n)))
+      (when (>= s MAX_N) (return))
+      (define c (* (choose (vector-ref rooted n) (- b br)) cnt))
+      (when (< (* l 2) s) (vector-inc! unrooted s c))
+      (when (= b BRANCH) (return))
+      (vector-inc! rooted s c)
+      (for ([m (in-range (sub1 n) 0 -1)]) (tree b m c s l)))))
+
+(define (bicenter s)
+  (when (even? s)
+    (vector-inc! unrooted s (* (vector-ref rooted (/ s 2))
+                               (add1 (vector-ref rooted (/ s 2)))
+                               1/2))))
+
+(for ([n (in-range 1 MAX_N)])
+  (tree 0 n 1 1 n)
+  (bicenter n)
+  (printf "~a: ~a\n" n (vector-ref unrooted n)))