Robert Smith committed 9c60df5

subsequence code

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Files changed (1)

       (comb1 (coerce x 'list) nil m)
+(defun scan-subsequences (f x m)
+  (labels ((comb1 (l c m)
+             (when (>= (length l) m)
+               (when (zerop m)
+                 (funcall f 
+                          (coerce (reverse c) 'vector))
+                 (return-from comb1))
+               (comb1 (cdr l) c m)
+               (comb1 (cdr l) (cons (first l) c) (1- m)))))
+    (comb1 (coerce x 'list) nil m)))
+(defun count-subsequences (x n)
+  (let ((c 0))
+    (scan-subsequences (lambda (s)
+                         (declare (ignore s))
+                         (incf c))
+                       x
+                       n)
+    c))
 (defun permutation-matches-p (perm pattern)
   "Does the permutation PERM have a subsequence which matches the
 pattern PATTERN?"