Sync luhn (#780)

exercises/practice/luhn/.docs/instructions.md

@@ -2,35 +2,31 @@
 
 Given a number determine whether or not it is valid per the Luhn formula.
 
-The [Luhn algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) is
-a simple checksum formula used to validate a variety of identification
-numbers, such as credit card numbers and Canadian Social Insurance
-Numbers.
+The [Luhn algorithm][luhn] is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.
 
 The task is to check if a given string is valid.
 
-Validating a Number
-------
+## Validating a Number
 
-Strings of length 1 or less are not valid. Spaces are allowed in the input,
-but they should be stripped before checking. All other non-digit characters
-are disallowed.
+Strings of length 1 or less are not valid.
+Spaces are allowed in the input, but they should be stripped before checking.
+All other non-digit characters are disallowed.
 
-## Example 1: valid credit card number
+### Example 1: valid credit card number
 
 ```text
 4539 3195 0343 6467
 ```
 
-The first step of the Luhn algorithm is to double every second digit,
-starting from the right. We will be doubling
+The first step of the Luhn algorithm is to double every second digit, starting from the right.
+We will be doubling
 
 ```text
 4_3_ 3_9_ 0_4_ 6_6_
 ```
 
-If doubling the number results in a number greater than 9 then subtract 9
-from the product. The results of our doubling:
+If doubling the number results in a number greater than 9 then subtract 9 from the product.
+The results of our doubling:
 
 ```text
 8569 6195 0383 3437
@@ -42,9 +38,10 @@ Then sum all of the digits:
 8+5+6+9+6+1+9+5+0+3+8+3+3+4+3+7 = 80
 ```
 
-If the sum is evenly divisible by 10, then the number is valid. This number is valid!
+If the sum is evenly divisible by 10, then the number is valid.
+This number is valid!
 
-## Example 2: invalid credit card number
+### Example 2: invalid credit card number
 
 ```text
 8273 1232 7352 0569
@@ -63,3 +60,5 @@ Sum the digits
 ```
 
 57 is not evenly divisible by 10, so this number is not valid.
+
+[luhn]: https://en.wikipedia.org/wiki/Luhn_algorithm

exercises/practice/luhn/.meta/example.php

@@ -1,50 +1,32 @@
 <?php
 
-/*
- * By adding type hints and enabling strict type checking, code can become
- * easier to read, self-documenting and reduce the number of potential bugs.
- * By default, type declarations are non-strict, which means they will attempt
- * to change the original type to match the type specified by the
- * type-declaration.
- *
- * In other words, if you pass a string to a function requiring a float,
- * it will attempt to convert the string value to a float.
- *
- * To enable strict mode, a single declare directive must be placed at the top
- * of the file.
- * This means that the strictness of typing is configured on a per-file basis.
- * This directive not only affects the type declarations of parameters, but also
- * a function's return type.
- *
- * For more info review the Concept on strict type checking in the PHP track
- * <link>.
- *
- * To disable strict typing, comment out the directive below.
- */
-
 declare(strict_types=1);
 
-function isValid($candidate)
+function isValid(string $candidate): bool
 {
-    $sanitizedCandidate = str_replace(" ", "", $candidate) ;
+    $sanitizedCandidate = str_replace(" ", "", $candidate);
 
     if (strlen($sanitizedCandidate) <= 1 || !ctype_digit($sanitizedCandidate)) {
-        return false ;
+        return false;
     }
 
-    $reversseCandidate = strrev($sanitizedCandidate) ;
-    $sum = 0 ;
+    $reverseCandidate = strrev($sanitizedCandidate);
+    $sum = 0;
+
+    for ($i = 0; $i < strlen($reverseCandidate); $i++) {
+        $digit = intval($reverseCandidate[$i]);
 
-    for ($i = 1; $i < strlen($reversseCandidate); $i += 2) {
-        $digit = 2 * intval($reversseCandidate[$i]) ;
+        // Double every second digit starting from the second position
+        if ($i % 2 != 0) {
+            $digit *= 2;
 
-        if ($digit > 9) {
-            $digit -= 9 ;
+            if ($digit > 9) {
+                $digit -= 9;
+            }
         }
 
-        $sum += $digit ;
-        $sum += intval($reversseCandidate[$i - 1]) ;
+        $sum += $digit;
     }
 
-    return $sum % 10 == 0 ;
+    return $sum % 10 === 0;
 }

exercises/practice/luhn/.meta/tests.toml

@@ -1,6 +1,13 @@
-# This is an auto-generated file. Regular comments will be removed when this
-# file is regenerated. Regenerating will not touch any manually added keys,
-# so comments can be added in a "comment" key.
+# 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.
 
 [792a7082-feb7-48c7-b88b-bbfec160865e]
 description = "single digit strings can not be valid"
@@ -26,6 +33,9 @@ description = "invalid credit card"
 [20e67fad-2121-43ed-99a8-14b5b856adb9]
 description = "invalid long number with an even remainder"
 
+[7e7c9fc1-d994-457c-811e-d390d52fba5e]
+description = "invalid long number with a remainder divisible by 5"
+
 [ad2a0c5f-84ed-4e5b-95da-6011d6f4f0aa]
 description = "valid number with an even number of digits"
 
@@ -50,8 +60,17 @@ description = "more than a single zero is valid"
 [ab56fa80-5de8-4735-8a4a-14dae588663e]
 description = "input digit 9 is correctly converted to output digit 9"
 
+[b9887ee8-8337-46c5-bc45-3bcab51bc36f]
+description = "very long input is valid"
+
+[8a7c0e24-85ea-4154-9cf1-c2db90eabc08]
+description = "valid luhn with an odd number of digits and non zero first digit"
+
 [39a06a5a-5bad-4e0f-b215-b042d46209b1]
 description = "using ascii value for non-doubled non-digit isn't allowed"
 
 [f94cf191-a62f-4868-bc72-7253114aa157]
 description = "using ascii value for doubled non-digit isn't allowed"
+
+[8b72ad26-c8be-49a2-b99c-bcc3bf631b33]
+description = "non-numeric, non-space char in the middle with a sum that's divisible by 10 isn't allowed"