Luhn 筆記

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Luhn 簡單的驗證身份證號碼的公式,用來驗證身分證和信用卡 a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.

從右邊開始,每2的倍數,就乘以2,如果超過9,則將數字減去9,然後所有數字的合可以整除10,驗證通過

4539 1488 0343 6467 -> 4_3_1_8_0_4_66 ->8569 2478 0383 3437

8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 -> 80/10=0

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/* 從右邊開始,每2的倍數,就乘以2,如果超過9,則將數字減去9,然後所有數字的合可以整除10,驗證通過

4539 1488 0343 6467 -> 4_3_1_8_0_4_6_6_ ->8569 2478 0383 3437

8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80 -> 80/10=0
*/

func Valid(input string) bool {

    sum := 0

    input = strings.Replace(input, " ", "", -1)

    inputSlice := strings.Split(input, "")

    if len(inputSlice) <= 1 {
        return false
    }
    //fmt.Println(inputSlice)

    for i := 0; i < len(inputSlice); i++ {
        if i%2 != 0 {
            temp, _ := multiply(inputSlice[i])
            inputSlice[i] = strconv.Itoa(temp)
        }
        temp2, _ := strconv.Atoi(inputSlice[i])
        fmt.Println(temp2)
        sum += temp2
    }
    fmt.Println(inputSlice)

    fmt.Println(sum)

    if sum%10 == 0 {
        return true
    }

    return false
}

func multiply(input string) (int, error) {
    doubleInput, err := strconv.Atoi(input)

    if err != nil {
        return 0, errors.New("input is not int")
    }

    doubleInput = doubleInput * 2

    if doubleInput > 9 {
        doubleInput = doubleInput - 9
    }

    return doubleInput, nil
}

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solution