Add largest-series-product exercise

config.json

@@ -420,6 +420,18 @@
           "strings"
         ]
       },
+      {
+        "slug": "largest-series-product",
+        "name": "Largest Series Product",
+        "uuid": "91b2ba1a-8995-4c5c-9682-1ef462cbcbf5",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4,
+        "topics": [
+          "control_flow_loops",
+          "strings"
+        ]
+      },
       {
         "slug": "affine-cipher",
         "name": "Affine Cipher",

exercises/practice/largest-series-product/.docs/instructions.md

@@ -0,0 +1,26 @@
+# Instructions
+
+Your task is to look for patterns in the long sequence of digits in the encrypted signal.
+
+The technique you're going to use here is called the largest series product.
+
+Let's define a few terms, first.
+
+- **input**: the sequence of digits that you need to analyze
+- **series**: a sequence of adjacent digits (those that are next to each other) that is contained within the input
+- **span**: how many digits long each series is
+- **product**: what you get when you multiply numbers together
+
+Let's work through an example, with the input `"63915"`.
+
+- To form a series, take adjacent digits in the original input.
+- If you are working with a span of `3`, there will be three possible series:
+  - `"639"`
+  - `"391"`
+  - `"915"`
+- Then we need to calculate the product of each series:
+  - The product of the series `"639"` is 162 (`6 × 3 × 9 = 162`)
+  - The product of the series `"391"` is 27 (`3 × 9 × 1 = 27`)
+  - The product of the series `"915"` is 45 (`9 × 1 × 5 = 45`)
+- 162 is bigger than both 27 and 45, so the largest series product of `"63915"` is from the series `"639"`.
+  So the answer is **162**.

exercises/practice/largest-series-product/.docs/introduction.md

@@ -0,0 +1,5 @@
+# Introduction
+
+You work for a government agency that has intercepted a series of encrypted communication signals from a group of bank robbers.
+The signals contain a long sequence of digits.
+Your team needs to use various digital signal processing techniques to analyze the signals and identify any patterns that may indicate the planning of a heist.

exercises/practice/largest-series-product/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "keiravillekode"
+  ],
+  "files": {
+    "solution": [
+      "largest-series-product.el"
+    ],
+    "test": [
+      "largest-series-product-test.el"
+    ],
+    "example": [
+      ".meta/example.el"
+    ]
+  },
+  "blurb": "Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.",
+  "source": "A variation on Problem 8 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=8"
+}

exercises/practice/largest-series-product/.meta/example.el

@@ -0,0 +1,26 @@
+;;; largest-series-product.el --- Largest Series Product (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'cl-lib)
+
+(defun largest-product (digits span)
+  (when (< span 0)
+    (error "span must not be negative"))
+  (when (> span (length digits))
+    (error "span must be smaller than string length"))
+  (unless (cl-every 'cl-digit-char-p (cl-coerce digits 'list))
+    (error "digits input must only contain digits"))
+  (let ((largest 0))
+    (dotimes (i (+ 1 (- (length digits) span)))
+      (let ((product 1))
+        (dotimes (j span)
+          (setq product (* product (cl-digit-char-p (aref digits (+ i j))))))
+        (when (< largest product)
+          (setq largest product))))
+    largest))
+
+(provide 'largest-series-product)
+;;; largest-series-product.el ends here

exercises/practice/largest-series-product/.meta/tests.toml

@@ -0,0 +1,60 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[7c82f8b7-e347-48ee-8a22-f672323324d4]
+description = "finds the largest product if span equals length"
+
+[88523f65-21ba-4458-a76a-b4aaf6e4cb5e]
+description = "can find the largest product of 2 with numbers in order"
+
+[f1376b48-1157-419d-92c2-1d7e36a70b8a]
+description = "can find the largest product of 2"
+
+[46356a67-7e02-489e-8fea-321c2fa7b4a4]
+description = "can find the largest product of 3 with numbers in order"
+
+[a2dcb54b-2b8f-4993-92dd-5ce56dece64a]
+description = "can find the largest product of 3"
+
+[673210a3-33cd-4708-940b-c482d7a88f9d]
+description = "can find the largest product of 5 with numbers in order"
+
+[02acd5a6-3bbf-46df-8282-8b313a80a7c9]
+description = "can get the largest product of a big number"
+
+[76dcc407-21e9-424c-a98e-609f269622b5]
+description = "reports zero if the only digits are zero"
+
+[6ef0df9f-52d4-4a5d-b210-f6fae5f20e19]
+description = "reports zero if all spans include zero"
+
+[5d81aaf7-4f67-4125-bf33-11493cc7eab7]
+description = "rejects span longer than string length"
+
+[06bc8b90-0c51-4c54-ac22-3ec3893a079e]
+description = "reports 1 for empty string and empty product (0 span)"
+
+[3ec0d92e-f2e2-4090-a380-70afee02f4c0]
+description = "reports 1 for nonempty string and empty product (0 span)"
+
+[6d96c691-4374-4404-80ee-2ea8f3613dd4]
+description = "rejects empty string and nonzero span"
+
+[7a38f2d6-3c35-45f6-8d6f-12e6e32d4d74]
+description = "rejects invalid character in digits"
+
+[5fe3c0e5-a945-49f2-b584-f0814b4dd1ef]
+description = "rejects negative span"
+include = false
+
+[c859f34a-9bfe-4897-9c2f-6d7f8598e7f0]
+description = "rejects negative span"
+reimplements = "5fe3c0e5-a945-49f2-b584-f0814b4dd1ef"

exercises/practice/largest-series-product/largest-series-product-test.el

@@ -0,0 +1,72 @@
+;;; largest-series-product-test.el --- Tests for Largest Series Product (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+(load-file "largest-series-product.el")
+(declare-function largest-product "largest-series-product.el" (digits span))
+
+
+(ert-deftest finds-the-largest-product-if-span-equals-length ()
+  (should (equal 18 (largest-product "29" 2))))
+
+
+(ert-deftest can-find-the-largest-product-of-2-with-numbers-in-order ()
+  (should (equal 72 (largest-product "0123456789" 2))))
+
+
+(ert-deftest can-find-the-largest-product-of-2 ()
+  (should (equal 48 (largest-product "576802143" 2))))
+
+
+(ert-deftest can-find-the-largest-product-of-3-with-numbers-in-order ()
+  (should (equal 504 (largest-product "0123456789" 3))))
+
+
+(ert-deftest can-find-the-largest-product-of-3 ()
+  (should (equal 270 (largest-product "1027839564" 3))))
+
+
+(ert-deftest can-find-the-largest-product-of-5-with-numbers-in-order ()
+  (should (equal 15120 (largest-product "0123456789" 5))))
+
+
+(ert-deftest can-get-the-largest-product-of-a-big-number ()
+  (should (equal 23520 (largest-product "73167176531330624919225119674426574742355349194934" 6))))
+
+
+(ert-deftest reports-zero-if-the-only-digits-are-zero ()
+  (should (equal 0 (largest-product "0000" 2))))
+
+
+(ert-deftest reports-zero-if-all-spans-include-zero ()
+  (should (equal 0 (largest-product "99099" 3))))
+
+
+(ert-deftest rejects-span-longer-than-string-length ()
+  (should-error (largest-product "123" 4)))
+
+
+(ert-deftest reports-1-for-empty-string-and-empty-product-zero-span ()
+  (should (equal 1 (largest-product "" 0))))
+
+
+(ert-deftest reports-1-for-nonempty-string-and-empty-product-zero-span ()
+  (should (equal 1 (largest-product "123" 0))))
+
+
+(ert-deftest rejects-empty-string-and-nonzero-span ()
+  (should-error (largest-product "" 1)))
+
+
+(ert-deftest rejects-invalid-character-in-digits ()
+  (should-error (largest-product "1234a5" 2)))
+
+
+(ert-deftest rejects-negative-span ()
+  (should-error (largest-product "12345" -1)))
+
+
+(provide 'largest-series-product-test)
+;;; largest-series-product-test.el ends here

exercises/practice/largest-series-product/largest-series-product.el

@@ -0,0 +1,13 @@
+;;; largest-series-product.el --- Largest Series Product (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(defun largest-product (digits span)
+ (error "Delete this S-Expression and write your own implementation"))
+
+
+(provide 'largest-series-product)
+;;; largest-series-product.el ends here