add raindrops and perfect-numbers

perfect-numbers/README.md

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+# Perfect Numbers
+
+Determine if a number is perfect, abundant, or deficient based on
+Nicomachus' (60 - 120 CE) classification scheme for natural numbers.
+
+The Greek mathematician [Nicomachus](https://en.wikipedia.org/wiki/Nicomachus) devised a classification scheme for natural numbers, identifying each as belonging uniquely to the categories of **perfect**, **abundant**, or **deficient** based on their [aliquot sum](https://en.wikipedia.org/wiki/Aliquot_sum). The aliquot sum is defined as the sum of the factors of a number not including the number itself. For example, the aliquot sum of 15 is (1 + 3 + 5) = 9
+
+- **Perfect**: aliquot sum = number 
+  - 6 is a perfect number because (1 + 2 + 3) = 6
+  - 28 is a perfect number because (1 + 2 + 4 + 7 + 14) = 28
+- **Abundant**: aliquot sum > number
+  - 12 is an abundant number because (1 + 2 + 3 + 4 + 6) = 16
+  - 24 is an abundant number because (1 + 2 + 3 + 4 + 6 + 8 + 12) = 36
+- **Deficient**: aliquot sum < number
+  - 8 is a deficient number because (1 + 2 + 4) = 7
+  - Prime numbers are deficient
+
+Implement a way to determine whether a given number is **perfect**. Depending on your language track, you may also need to implement a way to determine whether a given number is **abundant** or **deficient**.
+## Source
+
+Taken from Chapter 2 of Functional Thinking by Neal Ford. [http://shop.oreilly.com/product/0636920029687.do](http://shop.oreilly.com/product/0636920029687.do)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

perfect-numbers/perfect-numbers-test.el

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+;;; perfect-numbers-test.el --- Tests for perfect-numbers (exercism)
+
+;;; Commentary:
+
+;;; Code:
+
+(load-file "perfect-numbers.el")
+
+
+(ert-deftest no-perfect-numbers-in-1-to-5 ()
+    (should (equal (perfect-numbers 5) '())))
+
+(ert-deftest return-one-perfect-number-for-range-1-to-6 ()
+    (should (equal (perfect-numbers 6) '(6))))
+
+(ert-deftest return-3-perfect-numbers-for-range-1-to-1000 ()
+    (should (equal (perfect-numbers 1000) '(6 28 496))))
+
+(ert-deftest return-4-perfect-numbers-for-range-1-to-10000 ()
+    (should (equal (perfect-numbers 10000) '(6 28 496 8128))))
+
+
+(provide 'perfect-numbers)
+;;; perfect-numbers-test.el ends here

perfect-numbers/perfect-numbers.el

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+;;; perfect-numbers.el --- perfect-numbers Exercise (exercism)
+
+;;; Commentary:
+
+;;; Code:
+
+(defun perfect-numbers(x)
+  "Finds perfect numbers up to a given number"
+  (let ((result '())
+        (number x))
+    (while (>= number 2)
+      (if (perfect? number)
+          (setq result (cons number result)))
+      (setq number (1- number)))
+    result))
+
+(defun perfect?(x)
+  "Checks if a number is perfect"
+  (let ((upper-limit (1+ (/ x 2)))
+        (count 2)
+        (factors '(1)))
+    (while (<= count upper-limit)
+      (if (= (% x count) 0)
+          (setq factors (cons count factors)))
+      (setq count (1+ count)))
+    (= x (apply '+ factors))))
+
+
+(provide 'perfect-numbers)
+;;; perfect-numbers.el ends here

raindrops/README.md

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+# Raindrops
+
+Convert a number to a string, the contents of which depend on the number's factors.
+
+- If the number has 3 as a factor, output 'Pling'.
+- If the number has 5 as a factor, output 'Plang'.
+- If the number has 7 as a factor, output 'Plong'.
+- If the number does not have 3, 5, or 7 as a factor,
+  just pass the number's digits straight through.
+
+## Examples
+
+- 28's factors are 1, 2, 4, **7**, 14, 28.
+  - In raindrop-speak, this would be a simple "Plong".
+- 30's factors are 1, 2, **3**, **5**, 6, 10, 15, 30.
+  - In raindrop-speak, this would be a "PlingPlang".
+- 34 has four factors: 1, 2, 17, and 34.
+  - In raindrop-speak, this would be "34".
+## Source
+
+A variation on a famous interview question intended to weed out potential candidates. [http://jumpstartlab.com](http://jumpstartlab.com)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

raindrops/raindrops-test.el

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+;;; raindrops-test.el --- Tests for Raindrops (exercism)
+
+;;; Commentary:
+
+;;; Code:
+
+(load-file "raindrops.el")
+
+(ert-deftest test-1 ()
+  (should (equal "1"
+                 (convert 1))))
+
+(ert-deftest test-3 ()
+  (should (equal "Pling"
+                 (convert 3))))
+
+(ert-deftest test-5 ()
+  (should (equal "Plang"
+                 (convert 5))))
+
+(ert-deftest test-7 ()
+  (should (equal "Plong"
+                 (convert 7))))
+
+(ert-deftest test-6 ()
+  (should (equal "Pling"
+                 (convert 6))))
+
+(ert-deftest test-9 ()
+  (should (equal "Pling"
+                 (convert 9))))
+
+(ert-deftest test-10 ()
+  (should (equal "Plang"
+                 (convert 10))))
+
+(ert-deftest test-15 ()
+  (should (equal "PlingPlang"
+                 (convert 15))))
+
+(ert-deftest test-21 ()
+  (should (equal "PlingPlong"
+                 (convert 21))))
+
+(ert-deftest test-25 ()
+  (should (equal "Plang"
+                 (convert 25))))
+
+(ert-deftest test-35 ()
+  (should (equal "PlangPlong"
+                 (convert 35))))
+
+(ert-deftest test-49 ()
+  (should (equal "Plong"
+                 (convert 49))))
+
+(ert-deftest test-52 ()
+  (should (equal "52"
+                 (convert 52))))
+
+(ert-deftest test-105 ()
+  (should (equal "PlingPlangPlong"
+                 (convert 105))))
+
+(ert-deftest test-12121 ()
+  (should (equal "12121"
+                 (convert 12121))))
+
+(provide 'raindrops-test)
+;;; raindrops-test.el ends here

raindrops/raindrops.el

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+;;; raindrops.el --- Raindrops (exercism)
+
+;;; Commentary:
+
+;;; Code:
+
+
+(defun convert (n)
+  "Convert integer N to its raindrops string."
+  (let* ((raindrops '((3 . "Pling") (5 . "Plang") (7 . "Plong")))
+         (result (mapconcat #'(lambda (x) (let ((factor (car x))
+                                               (dropname (cdr x)))
+                                           (if (= (% n factor) 0)
+                                               dropname
+                                             "")))
+                           raindrops "")))
+    (if (string-equal "" result)
+        (number-to-string n)
+      result)))
+
+(provide 'raindrops)
+;;; raindrops.el ends here