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| 1 | +package me.premaseem.practiceRepeatation; |
| 2 | + |
| 3 | +/* |
| 4 | + |
| 5 | +Credit Card Validator |
| 6 | +Programming challenge description: |
| 7 | +Credit card numbers can be validated using an industry-standard algorithm called the Luhn Checksum: |
| 8 | + |
| 9 | +From the rightmost digit (the check digit), double the value of every second digit. The check digit is not doubled; the first digit doubled is immediately to the left of the check digit. If the result of this doubling operation is greater than 9 (e.g., 8 ×ばつ 2 = 16), then subtract 9 from the product (e.g., 16: 16 − 9 = 7, 18: 18 − 9 = 9). |
| 10 | +Take the sum of all the digits from step 1, both doubled and natural. |
| 11 | +If the total modulo 10 is equal to 0 (if the total ends in zero) then the number is valid according to the Luhn formula; otherwise it is not valid. |
| 12 | +The sum of all the digits in the third row is 67+x. If x = 3, then the modulo of 10 = 0, which means the credit card number is valid. |
| 13 | + |
| 14 | +Write a program that will validate credit card numbers using this algorithm and indicate the result. |
| 15 | + |
| 16 | +Input: |
| 17 | +A single line of input containing a potential credit card number |
| 18 | + |
| 19 | +Output: |
| 20 | +True if the credit card number is valid |
| 21 | +False if the credit card number is not valid |
| 22 | + |
| 23 | +Test Data: |
| 24 | +6011566926687256 - True |
| 25 | +370642420667124 - True |
| 26 | +5417438903761250 - True |
| 27 | +4518377421351212 - False |
| 28 | + |
| 29 | + */ |
| 30 | + |
| 31 | +import java.io.BufferedReader; |
| 32 | +import java.io.BufferedReader; |
| 33 | +import java.io.IOException; |
| 34 | +import java.io.InputStreamReader; |
| 35 | +import java.nio.charset.StandardCharsets; |
| 36 | +import java.util.ArrayList; |
| 37 | +import java.util.List; |
| 38 | + |
| 39 | +public class Credit_card_validator { |
| 40 | + |
| 41 | + public static void main(String[] args) throws IOException { |
| 42 | + InputStreamReader reader = new InputStreamReader(System.in, StandardCharsets.UTF_8); |
| 43 | + BufferedReader in = new BufferedReader(reader); |
| 44 | + String line; |
| 45 | + List<String> arr = new ArrayList(); |
| 46 | + while ((line = in.readLine()) != null) { |
| 47 | +// System.out.println(line); |
| 48 | + char[] ca = line.toCharArray(); |
| 49 | + System.out.println(ca); |
| 50 | + int os = 0; |
| 51 | + for (int i = ca.length-1; i>=0;i=i-2){ |
| 52 | + os += Integer.parseInt(""+ca[i]); |
| 53 | + } |
| 54 | + int es = 0; |
| 55 | + for (int i = ca.length-2; i>=0; i=i-2 ){ |
| 56 | + Integer d = Integer.parseInt(""+ca[i]) *2; |
| 57 | + d = d <10 ? d: d - 9; |
| 58 | + os += d; |
| 59 | + } |
| 60 | + |
| 61 | + System.out.println((os + es) % 10 == 0); |
| 62 | + |
| 63 | + } |
| 64 | + } |
| 65 | +} |
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