Data commit

Task/Middle-three-digits/Common-Lisp/middle-three-digits-1.lisp

@@ -0,0 +1,12 @@
+(defun mid3 (n)
+  (let ((a (abs n))
+        (hmd)) ; how many digits
+    (labels ((give (fmt &optional x y) (return-from mid3 (format nil fmt x y)))
+             (need (x) (give "Need ~a digits, not ~d." x hmd))
+             (nbr (n) (give "~3,'0d" n)))
+      (when (zerop n) (give "Zero is 1 digit"))
+      (setq hmd (truncate (1+ (log a 10))))
+      (cond ((< hmd 3) (need "3+"))
+            ((= hmd 3) (nbr a))
+            ((evenp hmd) (need "odd number of"))
+            (t (nbr (mod (truncate a (expt 10 (/ (- hmd 3) 2))) 1000)))))))

Task/Middle-three-digits/Common-Lisp/middle-three-digits-2.lisp

@@ -0,0 +1,4 @@
+(loop as n in '(123 12345 1234567 987654321
+                    10001 -10001 -123 -100 100 -12345
+                    1 2 -1 -10 2002 -2002 0)
+      do (format t "~d:~12t~a~%" n (mid3 n)))

Task/Middle-three-digits/Common-Lisp/middle-three-digits-3.lisp

@@ -0,0 +1,17 @@
+(defun mid3 (i)
+  (let ((ch-vec (coerce (format nil "~A" (abs i)) 'vector)))
+    (when (evenp (length ch-vec))
+      (return-from mid3
+        (format nil "Error: The number representation must have an odd ~
+                     number of digits.")))
+
+    (when (and (< i 100)
+               (> i -100))
+      (return-from mid3
+        (format nil "Error: Must be >= 100 or <= -100.")))
+    (let ((half (/ (1- (length ch-vec)) 2)))
+      (return-from mid3 (format nil "~A~A~A"
+                                   (elt ch-vec (1- half))
+                                   (elt ch-vec half)
+                                   (elt ch-vec (1+ half))))
+      )))

Task/Middle-three-digits/Common-Lisp/middle-three-digits-4.lisp

@@ -0,0 +1,31 @@
+(defun test-mid3 ()
+  (let ((test-lst (list 123
+                        12345
+                        1234567
+                        987654321
+                        10001
+                        -10001
+                        -123
+                        -100
+                        100
+                        -12345
+                        1
+                        2
+                        -1
+                        -10
+                        2002
+                        -2002
+                        0
+                        )))
+    (labels
+        ((run-tests (lst)
+           (cond ((null lst)
+                  nil)
+
+                 (t
+                  (format t "~A ~15T ~A~%" (first lst) (mid3 (first lst)))
+                  (run-tests (rest lst))))))
+
+      (run-tests test-lst)))
+  (values)
+  )