public static String addStr(String num1, String num2) { StringBuffer sb = new StringBuffer(); int sum = 0; int carry = 0; int i = num1.length() - 1, j = num2.length() - 1; while (i >= 0 || j >= 0 || carry > 0) { sum += carry;
if (i >= 0) { sum += num1.charAt(i) - '0'; i--; } if (j >= 0) { sum += num2.charAt(j) - '0'; j--; } sb.append(sum % 10); carry = sum / 10; sum = 0;