Add "Largest series product" exercise (#47)

* add largest-series-product scaffold

* sync docs

* add first solution for largest-series-product

* fix test names and add missing tests (make span signed int)

* add euler big number test

* refactor

* perform digit validation during calculation

* refactor + rename

* turn loop for finding max into recursion

* pass product struct to next_max_product

* turn product_from into recursive func

* Move new impl to example.cairo + revert lib.cairo to scaffold

* Add missing practices + add error-handling concept

* remove IndexOutOfBounds error

* refactor+additional test

concepts/error-handling/.meta/config.json

@@ -0,0 +1,7 @@
+{
+    "blurb": "<todo>",
+    "authors": [
+        "misicnenad"
+    ],
+    "contributors": []
+}

concepts/error-handling/about.md

@@ -0,0 +1 @@
+# Error Handling

concepts/error-handling/introduction.md

@@ -0,0 +1 @@
+# Introduction

concepts/error-handling/links.json

@@ -0,0 +1 @@
+[]

config.json

@@ -147,6 +147,18 @@
         ],
         "prerequisites": [],
         "difficulty": 4
+      },
+      {
+        "slug": "largest-series-product",
+        "name": "Largest Series Product",
+        "uuid": "d0cae4fa-22a8-4604-9f0f-f90751245ce3",
+        "practices": [
+          "enums",
+          "error-handling",
+          "control-flow"
+        ],
+        "prerequisites": [],
+        "difficulty": 4
       }
     ],
     "foregone": [
@@ -228,6 +240,11 @@
       "uuid": "6b6dafdb-7868-4089-855a-eb6735b5de5c",
       "slug": "arrays",
       "name": "Arrays"
+    },
+    {
+      "uuid": "cf49c14b-ed9a-4df6-a43a-3923e8489900",
+      "slug": "error-handling",
+      "name": "Error Handling"
     }
   ],
   "key_features": [

exercises/practice/armstrong-numbers/.docs/instructions.md

@@ -1,15 +1,13 @@
 # Instructions
 
-An [Armstrong number][armstrong-number] is a number that is the sum of its own
-digits each raised to the power of the number of digits.
+An [Armstrong number][armstrong-number] is a number that is the sum of its own digits each raised to the power of the number of digits.
 
 For example:
 
 - 9 is an Armstrong number, because `9 = 9^1 = 9`
 - 10 is _not_ an Armstrong number, because `10 != 1^2 + 0^2 = 1`
 - 153 is an Armstrong number, because: `153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153`
-- 154 is _not_ an Armstrong number, because:
-  `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
+- 154 is _not_ an Armstrong number, because: `154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190`
 
 Write some code to determine whether a number is an Armstrong number.
 

exercises/practice/beer-song/.docs/instructions.md

@@ -1,7 +1,6 @@
 # Instructions
 
-Recite the lyrics to that beloved classic, that field-trip favorite: 99 Bottles
-of Beer on the Wall.
+Recite the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.
 
 Note that not all verses are identical.
 

exercises/practice/hello-world/.docs/instructions.md

@@ -3,8 +3,7 @@
 The classical introductory exercise.
 Just say "Hello, World!".
 
-["Hello, World!"][hello-world] is the traditional first program for beginning
-programming in a new language or environment.
+["Hello, World!"][hello-world] is the traditional first program for beginning programming in a new language or environment.
 
 The objectives are simple:
 

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 +1,20 @@
+{
+  "authors": [
+    "misicnenad"
+  ],
+  "files": {
+    "solution": [
+      "src/lib.cairo",
+      "Scarb.toml"
+    ],
+    "test": [
+      "src/tests.cairo"
+    ],
+    "example": [
+      ".meta/example.cairo"
+    ]
+  },
+  "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.cairo

@@ -0,0 +1,112 @@
+#[derive(Drop, Debug, PartialEq)]
+pub enum Error {
+    SpanTooLong,
+    InvalidDigit: u8,
+    NegativeSpan,
+    IndexOutOfBounds
+}
+
+#[derive(Drop, Copy)]
+struct Product {
+    value: u64,
+    from: u32,
+}
+
+pub fn lsp(input: @ByteArray, span: i32) -> Result<u64, Error> {
+    // validate span
+    if span == 0 {
+        return Result::Ok(1);
+    }
+    if span < 0 {
+        return Result::Err(Error::NegativeSpan);
+    }
+
+    // shadowing to make span of unsigned type
+    let span: u32 = span.try_into().unwrap();
+
+    if span > input.len() {
+        return Result::Err(Error::SpanTooLong);
+    }
+
+    // calculate first max product
+    // use '?' to propagate the error if it occurred
+    let product = product_from(input, span, 0, span, Product { value: 1, from: 0 })?;
+
+    next_max_product(input, span, product.value, product)
+}
+
+fn product_from(
+    input: @ByteArray, span: u32, from: u32, remaining: u32, product: Product
+) -> Result<Product, Error> {
+    if remaining == 0 {
+        return Result::Ok(product);
+    }
+    if from + remaining > input.len() {
+        return Result::Ok(Product { value: 0, from });
+    }
+
+    let digit = input.at(from).try_into_digit()?;
+    if digit != 0 {
+        return product_from(
+            input,
+            span,
+            from + 1,
+            remaining - 1,
+            Product { value: product.value * digit, from: product.from }
+        );
+    } else {
+        return product_from(input, span, from + 1, span, Product { value: 1, from: from + 1 });
+    }
+}
+
+fn next_max_product(
+    input: @ByteArray, span: u32, max: u64, current_product: Product
+) -> Result<u64, Error> {
+    if current_product.from + span >= input.len() {
+        return Result::Ok(max);
+    }
+
+    // safe to unwrap, we already processed this digit before 
+    let reduced_value = current_product.value
+        / input.at(current_product.from).try_into_digit().unwrap();
+
+    let next_digit = input.at(current_product.from + span).try_into_digit()?;
+
+    let product = if next_digit == 0 {
+        product_from(
+            input,
+            span,
+            current_product.from + span + 1,
+            span,
+            Product { value: 1, from: current_product.from + span + 1 }
+        )?
+    } else {
+        Product { value: reduced_value * next_digit, from: current_product.from + 1 }
+    };
+
+    if product.value > max {
+        next_max_product(input, span, product.value, product)
+    } else {
+        next_max_product(input, span, max, product)
+    }
+}
+
+/// Helper functions
+#[generate_trait]
+impl ByteArrayCharToU64 of ByteArrayCharToU64Trait {
+    fn try_into_digit(self: @Option<u8>) -> Result<u64, Error> {
+        if let Option::Some(char) = (*self) {
+            // ASCII digits are characters 48 through 57
+            if 48 <= char && char <= 57 {
+                Result::Ok(char.into() - 48)
+            } else {
+                Result::Err(Error::InvalidDigit(char))
+            }
+        } else {
+            Result::Err(Error::IndexOutOfBounds)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;

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/Scarb.toml

@@ -0,0 +1,4 @@
+[package]
+name = "largest_series_product"
+version = "0.1.0"
+edition = "2023_11"