CODEWITHSUNDEEP
java
user14782699
user14782699

Reputation:

calculate Check Number in Java

Not sure if anyone can explain this to me or help me.

I have a 15 Digit Number of which I want to multiply each even number by 2 unless the even number is greater than 9. If it is this needs to be subtracted by 9 to give me an integer that again I can multiply by 2. Once I have all the even numbers multiplied by 2 i need to add them all together with the odd numbers.

Does that make sense.

UPDATE *** so i have a number say 49209999856459. for that number I am looking to get the even integer so for example the first even one would be 4 then the second would be 2 and so on.

If one of those even numbers are multiplied by 2 then it might be above 9 so I want to subtract 9 to then use the remainder as the even number in its place.

SO !!! Multiply by 2 the value of each even digit starting from index 0 and then each even index. In each case, if the resulting value is greater than 9, subtract 9 from it (which reduces larger values to a single digit). Leave the values of the digits at the odd indexes unchanged.

public String calculateCheckNumber()

  String firstFifteen = longNumber.substring(0,15) ;
  int i, checkSum = 0, totalSum = 0;
  for (i = 0; i<firstFifteen.length(); i += 2) {


while (i < 9)
        i *= 2;
 if   (i > 9)
       i -= 9 ;
       
}

Was one option I was trying but it honestly I cant seem to get my head around it.

Any Help would be greatly appreciated.

Upvotes: 2

Views: 300

Answers (1)

WJS
WJS

Reputation: 40034

Well, here is one approach. This uses the ternary (?:) operator to condense the operations. Edited base on clarification from the OP. The example you gave is actually a 14 digit string. But the following will work with any number of digits if they start out in a string. If you have a long value, then you can create the character array using:

long v = 49209999856459L;
char[] d = Long.toString(v).toCharArray();

Here is the main algorithm.

String s = "49209999856459";
int sum = 0;
char[] d = s.toCharArray();
for (int i = 0; i < d.length; i++) {
    int v = d[i] - '0';
    // The even digit will only be greater than 9 after
    // doubling if it is >= 5 before.
    sum += ((i % 2) == 1) ? v : (v >= 5) ? v+v-9 : v+v; 
}
System.out.println(sum);

Prints

86

Upvotes: 2

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