33 lines
502 B
Go
33 lines
502 B
Go
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package luhn
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import (
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"strconv"
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"github.com/neonxp/checksum"
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)
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// Check number is correct by luhn algorithm
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func Check(number string) error {
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mod := len(number) % 2
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sum := 0
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for i, ch := range number {
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num, err := strconv.Atoi(string(ch))
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if err != nil {
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return checksum.ErrInvalidNumber
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}
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if i%2 == mod {
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if num < 5 {
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sum += num * 2
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} else {
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sum += num*2 - 9
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}
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} else {
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sum += num
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}
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}
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if sum%10 != 0 {
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return checksum.ErrInvalidChecksum
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}
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return nil
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}
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