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Task/Greatest-subsequential-sum/EchoLisp/greatest-subsequential-sum.echolisp

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+(lib 'struct)
+(struct result (score starter))
+
+;; the score of  i in sequence ( .. i j ...)  is max (i , i + score (j))
+;; to compute score of (a b .. x y z) :
+;; start with score(z) and compute scores of y , z , ..c, b , a.
+;; this is O(n)
+
+;; return value of sub-sequence
+(define (max-max L into: result)
+(define value
+	(if
+	(empty? L) -Infinity
+	(max (first L)  (+ (first L) (max-max (cdr L) result )))))
+	
+    (when (> value (result-score result))
+		(set-result-score! result value) ;; remember best score
+		(set-result-starter! result L))  ;; and its location
+	value)
+
+;; return (best-score (best sequence))
+(define (max-seq L)
+	(define best (result -Infinity null))
+	(max-max L into: best)
+	(define score (result-score best))
+	
+	(list score
+	(for/list (( n (result-starter best)))
+			   #:break (zero? score)
+			   (set! score (- score n))
+			   n)))
+	
+(define L '(-1 -2 3 5 6 -2 -1 4 -4 2 -1))
+(max-seq L)
+    → (15 (3 5 6 -2 -1 4))