3.0 KiB
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5ea28156e79528a9ab248f27 | Luhn test of credit card numbers | 1 | 385284 | luhn-test-of-credit-card-numbers |
--description--
The Luhn test is used by some credit card companies to distinguish valid credit card numbers from what could be a random selection of digits.
Those companies using credit card numbers that can be validated by the Luhn test have numbers that pass the following test:
- Reverse the order of the digits in the number.
- Take the first, third, ... and every other odd digit in the reversed digits and sum them to form the partial sum s1
- Taking the second, fourth ... and every other even digit in the reversed digits:
- Multiply each digit by two and sum the digits if the answer is greater than nine to form partial sums for the even digits.
- Sum the partial sums of the even digits to form s2.
- If s1 + s2 ends in zero then the original number is in the form of a valid credit card number as verified by the Luhn test.
For example, if the trial number is 49927398716:
Reverse the digits:
61789372994
Sum the odd digits:
6 + 7 + 9 + 7 + 9 + 4 = 42 = s1
The even digits:
1, 8, 3, 2, 9
Two times each even digit:
2, 16, 6, 4, 18
Sum the digits of each multiplication:
2, 7, 6, 4, 9
Sum the last:
2 + 7 + 6 + 4 + 9 = 28 = s2
s1 + s2 = 70 which ends in zero which means that 49927398716 passes the Luhn test.
--instructions--
Write a function that will validate a number with the Luhn test. Return true if it's a valid number. Otherwise, return false.
--hints--
luhnTest
should be a function.
assert(typeof luhnTest === 'function');
luhnTest("4111111111111111")
should return a boolean.
assert(typeof luhnTest('4111111111111111') === 'boolean');
luhnTest("4111111111111111")
should return true
.
assert.equal(luhnTest('4111111111111111'), true);
luhnTest("4111111111111112")
should return false
.
assert.equal(luhnTest('4111111111111112'), false);
luhnTest("49927398716")
should return true
.
assert.equal(luhnTest('49927398716'), true);
luhnTest("49927398717")
should return false
.
assert.equal(luhnTest('49927398717'), false);
luhnTest("1234567812345678")
should return false
.
assert.equal(luhnTest('1234567812345678'), false);
luhnTest("1234567812345670")
should return true
.
assert.equal(luhnTest('1234567812345670'), true);
--seed--
--seed-contents--
function luhnTest(str) {
}
--solutions--
function luhnTest(str) {
var luhnArr = [0, 2, 4, 6, 8, 1, 3, 5, 7, 9];
var counter = 0;
var incNum;
var odd = false;
var temp = String(str).replace(/[^\d]/g, '');
if (temp.length == 0) return false;
for (var i = temp.length - 1; i >= 0; --i) {
incNum = parseInt(temp.charAt(i), 10);
counter += (odd = !odd) ? incNum : luhnArr[incNum];
}
return counter % 10 == 0;
}