complete luhn

luhn/.exercism/config.json

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+{
+  "blurb": "Given a number determine whether or not it is valid per the Luhn formula.",
+  "authors": [
+    "soniakeys"
+  ],
+  "contributors": [
+    "alebaffa",
+    "bitfield",
+    "da-edra",
+    "ekingery",
+    "ferhatelmas",
+    "hilary",
+    "kytrinyx",
+    "leenipper",
+    "michaelorr",
+    "petertseng",
+    "robphoenix",
+    "sebito91",
+    "tehsphinx"
+  ],
+  "files": {
+    "solution": [
+      "luhn.go"
+    ],
+    "test": [
+      "luhn_test.go"
+    ],
+    "example": [
+      ".meta/example.go"
+    ],
+    "editor": [
+      "cases_test.go"
+    ]
+  },
+  "source": "The Luhn Algorithm on Wikipedia",
+  "source_url": "http://en.wikipedia.org/wiki/Luhn_algorithm"
+}

luhn/.exercism/metadata.json

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+{"track":"go","exercise":"luhn","id":"7bbeac9d18bd4ddea3f7e1ed4cc1f5a5","url":"https://exercism.org/tracks/go/exercises/luhn","handle":"koheiyamayama","is_requester":true,"auto_approve":false}

luhn/HELP.md

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+# Help
+
+## Running the tests
+
+To run the tests run the command `go test` from within the exercise directory.
+
+If the test suite contains benchmarks, you can run these with the `--bench` and `--benchmem`
+flags:
+
+    go test -v --bench . --benchmem
+
+Keep in mind that each reviewer will run benchmarks on a different machine, with
+different specs, so the results from these benchmark tests may vary.
+
+## Submitting your solution
+
+You can submit your solution using the `exercism submit luhn.go` command.
+This command will upload your solution to the Exercism website and print the solution page's URL.
+
+It's possible to submit an incomplete solution which allows you to:
+
+- See how others have completed the exercise
+- Request help from a mentor
+
+## Need to get help?
+
+If you'd like help solving the exercise, check the following pages:
+
+- The [Go track's documentation](https://exercism.org/docs/tracks/go)
+- [Exercism's support channel on gitter](https://gitter.im/exercism/support)
+- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
+
+Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
+
+To get help if you're having trouble, you can use one of the following resources:
+
+- [How to Write Go Code](https://golang.org/doc/code.html)
+- [Effective Go](https://golang.org/doc/effective_go.html)
+- [Go Resources](http://golang.org/help)
+- [StackOverflow](http://stackoverflow.com/questions/tagged/go)

luhn/README.md

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+# Luhn
+
+Welcome to Luhn on Exercism's Go Track.
+If you need help running the tests or submitting your code, check out `HELP.md`.
+
+## Instructions
+
+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 task is to check if a given string is valid.
+
+## 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.
+
+### 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
+
+```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:
+
+```text
+8569 6195 0383 3437
+```
+
+Then sum all of the digits:
+
+```text
+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!
+
+### Example 2: invalid credit card number
+
+```text
+8273 1232 7352 0569
+```
+
+Double the second digits, starting from the right
+
+```text
+7253 2262 5312 0539
+```
+
+Sum the digits
+
+```text
+7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57
+```
+
+57 is not evenly divisible by 10, so this number is not valid.
+
+## Source
+
+### Created by
+
+- @soniakeys
+
+### Contributed to by
+
+- @alebaffa
+- @bitfield
+- @da-edra
+- @ekingery
+- @ferhatelmas
+- @hilary
+- @kytrinyx
+- @leenipper
+- @michaelorr
+- @petertseng
+- @robphoenix
+- @sebito91
+- @tehsphinx
+
+### Based on
+
+The Luhn Algorithm on Wikipedia - http://en.wikipedia.org/wiki/Luhn_algorithm

luhn/cases_test.go

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+package luhn
+
+// Source: exercism/problem-specifications
+// Commit: f375a46 luhn: Update non-ASCII test case
+// Problem Specifications Version: 1.6.1
+
+var testCases = []struct {
+	description string
+	input       string
+	ok          bool
+}{
+	{
+		"single digit strings can not be valid",
+		"1",
+		false,
+	},
+	{
+		"a single zero is invalid",
+		"0",
+		false,
+	},
+	{
+		"a simple valid SIN that remains valid if reversed",
+		"059",
+		true,
+	},
+	{
+		"a simple valid SIN that becomes invalid if reversed",
+		"59",
+		true,
+	},
+	{
+		"a valid Canadian SIN",
+		"055 444 285",
+		true,
+	},
+	{
+		"invalid Canadian SIN",
+		"055 444 286",
+		false,
+	},
+	{
+		"invalid credit card",
+		"8273 1232 7352 0569",
+		false,
+	},
+	{
+		"valid number with an even number of digits",
+		"095 245 88",
+		true,
+	},
+	{
+		"valid number with an odd number of spaces",
+		"234 567 891 234",
+		true,
+	},
+	{
+		"valid strings with a non-digit added at the end become invalid",
+		"059a",
+		false,
+	},
+	{
+		"valid strings with punctuation included become invalid",
+		"055-444-285",
+		false,
+	},
+	{
+		"valid strings with symbols included become invalid",
+		"055# 444$ 285",
+		false,
+	},
+	{
+		"single zero with space is invalid",
+		" 0",
+		false,
+	},
+	{
+		"more than a single zero is valid",
+		"0000 0",
+		true,
+	},
+	{
+		"input digit 9 is correctly converted to output digit 9",
+		"091",
+		true,
+	},
+	{
+		"valid number with an odd number of digits and non-zero first digit",
+		"109",
+		true,
+	},
+	{
+		"using ascii value for non-doubled non-digit isn't allowed",
+		"055b 444 285",
+		false,
+	},
+	{
+		"using ascii value for doubled non-digit isn't allowed",
+		":9",
+		false,
+	},
+}

luhn/go.mod

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+module luhn
+
+go 1.16

luhn/luhn.go

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+package luhn
+
+import (
+	"strconv"
+	"strings"
+)
+
+func Valid(id string) bool {
+	id = strings.ReplaceAll(id, " ", "")
+
+	if len(id) <= 1 {
+		return false
+	}
+
+	ids := strings.Split(id, "")
+	sum := 0
+
+	for i := 1; i <= len(ids); i++ {
+		n, e := strconv.Atoi(ids[len(ids)-i])
+
+		if e != nil {
+			return false
+		}
+
+		if i%2 == 0 {
+			n *= 2
+
+			if 9 < n {
+				sum += n - 9
+			} else {
+				sum += n
+			}
+		} else {
+			sum += n
+		}
+	}
+
+	return sum%10 == 0
+}

luhn/luhn_test.go

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+package luhn
+
+import "testing"
+
+func TestValid(t *testing.T) {
+	for _, test := range testCases {
+		if ok := Valid(test.input); ok != test.ok {
+			t.Fatalf("Valid(%s): %s\n\t Expected: %t\n\t Got: %t", test.input, test.description, test.ok, ok)
+		}
+	}
+}
+
+func BenchmarkValid(b *testing.B) {
+	if testing.Short() {
+		b.Skip("skipping benchmark in short mode.")
+	}
+	for i := 0; i < b.N; i++ {
+		Valid("2323 2005 7766 3554")
+	}
+}