Add reg. integer and arbitary long integer

Problem: Add regular integer and arbitrary long integer (which is not fit in regular integer). Let's assume arbitrary long integer is available in a string.


Solution:

public class LongNumSum {

     

    public String sum(String a, String b){

        int maxSize = Math.max(a.length(), b.length());

        int minSize = Math.min(a.length(), b.length());

         

        char[] sumArr = new char[maxSize+1];

        int carry = 0;

        int i=a.length()-1;

        int j=b.length()-1;

        int k=maxSize;

        for(int count=0; count<minSize; i--, j--, count++) {

            int val = a.charAt(i)-'0' + b.charAt(j)-'0' + carry;

            if(val > 9) {

                val = val%10;

                carry = 1;

            }

            else {

                carry = 0;

            }

            sumArr[k--] = (char)('0'+val);         

        }

         

        while(i>=0){

            int val = a.charAt(i)-'0' + carry;

            if(val > 9) {

                val = val%10;

                carry = 1;

            }

            else {

                carry = 0;             

            }

            sumArr[k--] = (char)('0'+val);         

            i--;

        }

         

        while(j>=0){

            int val = b.charAt(j)-'0' + carry;

            if(val > 9) {

                val = val%10;

                carry = 1;

            }

            else {

                carry = 0;             

            }

            sumArr[k--] = (char)('0'+val);         

            j--;

        }

     

        if(carry == 1) {

            sumArr[0] = '1';

        } else {           

            System.arraycopy(sumArr, 1, sumArr, 0, maxSize-1);

        }

        return String.valueOf(sumArr);

    }

     

     

    public String sumLongNums(int regInt, String arbInt){      

        String rIntStr = Integer.toString(regInt);

        String sum = sum(rIntStr, arbInt);     

        return sum;    

    }

     

    /**

     * @param args

     */

    public static void main(String[] args) {

        // TODO Auto-generated method stub

         

        LongNumSum l = new LongNumSum();

        System.out.println(l.sumLongNums(123, "789"));

         

        System.out.println(l.sumLongNums(123, "99999"));

         

        System.out.println(l.sumLongNums(9999, "456"));

         

        System.out.println(l.sumLongNums(123, "23958735786483975938759835873597395"));

 

    }

 

}