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Add largest-series-product exercise (#418)
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keiravillekode authored Sep 5, 2024
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8 changes: 8 additions & 0 deletions config.json
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],
"difficulty": 1
},
{
"slug": "largest-series-product",
"name": "Largest Series Product",
"uuid": "1bc27002-2daa-4e09-b4a6-65053291c1dd",
"practices": [],
"prerequisites": [],
"difficulty": 4
},
{
"slug": "hamming",
"name": "Hamming",
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26 changes: 26 additions & 0 deletions exercises/practice/largest-series-product/.docs/instructions.md
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# 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**.
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# 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.
19 changes: 19 additions & 0 deletions exercises/practice/largest-series-product/.meta/config.json
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{
"authors": [
"keiravillekode"
],
"files": {
"solution": [
"largest_series_product.zig"
],
"test": [
"test_largest_series_product.zig"
],
"example": [
".meta/example.zig"
]
},
"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"
}
42 changes: 42 additions & 0 deletions exercises/practice/largest-series-product/.meta/example.zig
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pub const SeriesError = error{
InvalidCharacter,
NegativeSpan,
InsufficientDigits,
};

pub fn largestProduct(digits: []const u8, span: i32) SeriesError!u64 {
for (digits) |ch| {
const units: u8 = ch -% '0';
if (units > 9) {
return SeriesError.InvalidCharacter;
}
}

if (span < 0) {
return SeriesError.NegativeSpan;
}

if (span == 0) {
return 1;
}

const size: u64 = @intCast(span);

if (digits.len < size) {
return SeriesError.InsufficientDigits;
}

var result: u64 = 0;
for (0..(digits.len + 1 - size)) |begin| {
var product: u64 = 1;
for (digits[begin..(begin + size)]) |ch| {
product *= ch -% '0';
}

if (result < product) {
result = product;
}
}

return result;
}
60 changes: 60 additions & 0 deletions exercises/practice/largest-series-product/.meta/tests.toml
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# 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"
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pub const SeriesError = error{
InvalidCharacter,
NegativeSpan,
InsufficientDigits,
};

pub fn largestProduct(digits: []const u8, span: i32) SeriesError!u64 {
_ = digits;
_ = span;
@compileError("please implement the largestProduct function");
}
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const std = @import("std");
const testing = std.testing;

const largest_series_product = @import("largest_series_product.zig");

test "finds the largest product if span equals length" {
const expected: u64 = 18;
const actual = try largest_series_product.largestProduct("29", 2);
try testing.expectEqual(expected, actual);
}

test "can find the largest product of 2 with numbers in order" {
const expected: u64 = 72;
const actual = try largest_series_product.largestProduct("0123456789", 2);
try testing.expectEqual(expected, actual);
}

test "can find the largest product of 2" {
const expected: u64 = 48;
const actual = try largest_series_product.largestProduct("576802143", 2);
try testing.expectEqual(expected, actual);
}

test "can find the largest product of 3 with numbers in order" {
const expected: u64 = 504;
const actual = try largest_series_product.largestProduct("0123456789", 3);
try testing.expectEqual(expected, actual);
}

test "can find the largest product of 3" {
const expected: u64 = 270;
const actual = try largest_series_product.largestProduct("1027839564", 3);
try testing.expectEqual(expected, actual);
}

test "can find the largest product of 5 with numbers in order" {
const expected: u64 = 15120;
const actual = try largest_series_product.largestProduct("0123456789", 5);
try testing.expectEqual(expected, actual);
}

test "can get the largest product of a big number" {
const expected: u64 = 23520;
const actual = try largest_series_product.largestProduct("73167176531330624919225119674426574742355349194934", 6);
try testing.expectEqual(expected, actual);
}

test "reports zero if the only digits are zero" {
const expected: u64 = 0;
const actual = try largest_series_product.largestProduct("0000", 2);
try testing.expectEqual(expected, actual);
}

test "reports zero if all spans include zero" {
const expected: u64 = 0;
const actual = try largest_series_product.largestProduct("99099", 3);
try testing.expectEqual(expected, actual);
}

test "rejects span longer than string length" {
const actual = largest_series_product.largestProduct("123", 4);
try testing.expectError(largest_series_product.SeriesError.InsufficientDigits, actual);
}

test "reports 1 for empty string and empty product (0 span)" {
const expected: u64 = 1;
const actual = try largest_series_product.largestProduct("", 0);
try testing.expectEqual(expected, actual);
}

test "reports 1 for nonempty string and empty product (0 span)" {
const expected: u64 = 1;
const actual = try largest_series_product.largestProduct("123", 0);
try testing.expectEqual(expected, actual);
}

test "rejects empty string and nonzero span" {
const actual = largest_series_product.largestProduct("", 1);
try testing.expectError(largest_series_product.SeriesError.InsufficientDigits, actual);
}

test "rejects invalid character in digits" {
const actual = largest_series_product.largestProduct("1234a5", 2);
try testing.expectError(largest_series_product.SeriesError.InvalidCharacter, actual);
}

test "rejects negative span" {
const actual = largest_series_product.largestProduct("12345", -1);
try testing.expectError(largest_series_product.SeriesError.NegativeSpan, actual);
}

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