Luhn Algorithm
Level 6
10 Points
Instructions
Determine whether a number is valid according to the Luhn formula.
The number will be provided as a string.
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.
Examples
Valid credit card number
The number to be checked is 4539 3195 0343 6467.
The first step of the Luhn algorithm is to start at the end of the number and double every second digit, beginning with the second digit from the right and moving left.
4539 3195 0343 6467
↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ (double these)If the result of doubling a digit is greater than 9, we subtract 9 from that result. We end up with:
8569 6195 0383 3437Finally, we sum all digits. If the sum is evenly divisible by 10, the original number is valid.
8 + 5 + 6 + 9 + 6 + 1 + 9 + 5 + 0 + 3 + 8 + 3 + 3 + 4 + 3 + 7 = 8080 is evenly divisible by 10, so number 4539 3195 0343 6467 is valid!
Invalid Canadian SIN
The number to be checked is 066 123 478.
We start at the end of the number and double every second digit, beginning with the second digit from the right and moving left.
066 123 478
↑ ↑ ↑ ↑ (double these)If the result of doubling a digit is greater than 9, we subtract 9 from that result. We end up with:
036 226 458We sum the digits:
0 + 3 + 6 + 2 + 2 + 6 + 4 + 5 + 8 = 3636 is not evenly divisible by 10, so number 066 123 478 is not valid!
Luhn Algorithm
Level 6
10 Points
Instructions
Determine whether a number is valid according to the Luhn formula.
The number will be provided as a string.
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.
Examples
Valid credit card number
The number to be checked is 4539 3195 0343 6467.
The first step of the Luhn algorithm is to start at the end of the number and double every second digit, beginning with the second digit from the right and moving left.
4539 3195 0343 6467
↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ (double these)If the result of doubling a digit is greater than 9, we subtract 9 from that result. We end up with:
8569 6195 0383 3437Finally, we sum all digits. If the sum is evenly divisible by 10, the original number is valid.
8 + 5 + 6 + 9 + 6 + 1 + 9 + 5 + 0 + 3 + 8 + 3 + 3 + 4 + 3 + 7 = 8080 is evenly divisible by 10, so number 4539 3195 0343 6467 is valid!
Invalid Canadian SIN
The number to be checked is 066 123 478.
We start at the end of the number and double every second digit, beginning with the second digit from the right and moving left.
066 123 478
↑ ↑ ↑ ↑ (double these)If the result of doubling a digit is greater than 9, we subtract 9 from that result. We end up with:
036 226 458We sum the digits:
0 + 3 + 6 + 2 + 2 + 6 + 4 + 5 + 8 = 3636 is not evenly divisible by 10, so number 066 123 478 is not valid!