largest-series-product

config.json

@@ -342,6 +342,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "largest-series-product",
+        "name": "Largest Series Product",
+        "uuid": "d56c9861-434c-4299-b2ce-aa067a6d965f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ]
   },

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

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "largest_series_product.moon"
+    ],
+    "test": [
+      "largest_series_product_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "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.moon

@@ -0,0 +1,18 @@
+import fold from require 'moon'
+
+product = (...) -> fold {1, ...}, (p, d) -> p * d
+
+refute = (cond, msg) -> assert not cond, msg
+
+{
+  largest_product: (digits, span) ->
+    return 1 if span == 0
+
+    assert span >= 0, 'span must not be negative'
+    assert span <= #digits, 'span must not exceed string length'
+    refute digits\find('[^%d]'), 'digits input must only contain digits'
+
+    ds = [tonumber c for c in digits\gmatch('.')]
+    prods = [product table.unpack(ds, i, i + span - 1) for i = 1, #ds - (span - 1)]
+    math.max table.unpack prods
+}

exercises/practice/largest-series-product/.meta/spec_generator.moon

@@ -0,0 +1,20 @@
+{
+  module_imports: {'largest_product'},
+
+  generate_test: (case, level) ->
+    lines = {}
+    switch type(case.expected)
+      when 'number'
+        table.insert lines, "-- #{line}" for line in *(case.comments or {})
+        table.insert lines, line for line in *{
+          "result = largest_product #{quote case.input.digits}, #{case.input.span}",
+          "assert.are.equal #{case.expected}, result"
+        }
+      when 'table'
+        lines = {
+          "f = -> largest_product #{quote case.input.digits}, #{case.input.span}",
+          "assert.has.errors f, #{quote case.expected.error}"
+        }
+
+    table.concat [indent line, level for line in *lines], '\n'
+}

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

@@ -0,0 +1,70 @@
+# 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"
+include = false
+
+[0ae1ce53-d9ba-41bb-827f-2fceb64f058b]
+description = "rejects span longer than string length"
+reimplements = "5d81aaf7-4f67-4125-bf33-11493cc7eab7"
+
+[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"
+include = false
+
+[6cf66098-a6af-4223-aab1-26aeeefc7402]
+description = "rejects empty string and nonzero span"
+reimplements = "6d96c691-4374-4404-80ee-2ea8f3613dd4"
+
+[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.moon

@@ -0,0 +1,4 @@
+{
+  largest_product: (digits, span) ->
+    error 'Implement me'
+}

exercises/practice/largest-series-product/largest_series_product_spec.moon

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+import largest_product from require 'largest_series_product'
+
+describe 'largest-series-product', ->
+  it 'finds the largest product if span equals length', ->
+    result = largest_product '29', 2
+    assert.are.equal 18, result
+
+  pending 'can find the largest product of 2 with numbers in order', ->
+    result = largest_product '0123456789', 2
+    assert.are.equal 72, result
+
+  pending 'can find the largest product of 2', ->
+    result = largest_product '576802143', 2
+    assert.are.equal 48, result
+
+  pending 'can find the largest product of 3 with numbers in order', ->
+    result = largest_product '0123456789', 3
+    assert.are.equal 504, result
+
+  pending 'can find the largest product of 3', ->
+    result = largest_product '1027839564', 3
+    assert.are.equal 270, result
+
+  pending 'can find the largest product of 5 with numbers in order', ->
+    result = largest_product '0123456789', 5
+    assert.are.equal 15120, result
+
+  pending 'can get the largest product of a big number', ->
+    result = largest_product '73167176531330624919225119674426574742355349194934', 6
+    assert.are.equal 23520, result
+
+  pending 'reports zero if the only digits are zero', ->
+    result = largest_product '0000', 2
+    assert.are.equal 0, result
+
+  pending 'reports zero if all spans include zero', ->
+    result = largest_product '99099', 3
+    assert.are.equal 0, result
+
+  pending 'rejects span longer than string length', ->
+    f = -> largest_product '123', 4
+    assert.has.errors f, 'span must not exceed string length'
+
+  pending 'reports 1 for empty string and empty product (0 span)', ->
+    -- There may be some confusion about whether this should be 1 or error.
+    -- The reasoning for it being 1 is this:
+    -- There is one 0-character string contained in the empty string.
+    -- That's the empty string itself.
+    -- The empty product is 1 (the identity for multiplication).
+    -- Therefore LSP('', 0) is 1.
+    -- It's NOT the case that LSP('', 0) takes max of an empty list.
+    -- So there is no error.
+    -- Compare against LSP('123', 4):
+    -- There are zero 4-character strings in '123'.
+    -- So LSP('123', 4) really DOES take the max of an empty list.
+    -- So LSP('123', 4) errors and LSP('', 0) does NOT.
+    result = largest_product '', 0
+    assert.are.equal 1, result
+
+  pending 'reports 1 for nonempty string and empty product (0 span)', ->
+    -- As above, there is one 0-character string in '123'.
+    -- So again no error. It's the empty product, 1.
+    result = largest_product '123', 0
+    assert.are.equal 1, result
+
+  pending 'rejects empty string and nonzero span', ->
+    f = -> largest_product '', 1
+    assert.has.errors f, 'span must not exceed string length'
+
+  pending 'rejects invalid character in digits', ->
+    f = -> largest_product '1234a5', 2
+    assert.has.errors f, 'digits input must only contain digits'
+
+  pending 'rejects negative span', ->
+    f = -> largest_product '12345', -1
+    assert.has.errors f, 'span must not be negative'