private static Node SumForward(Node n1, Node n2)
{
if (n1 == null || n2 == null)
{
return(null);
}
// Length n1, n2
var length1 = n1.Length();
var length2 = n2.Length();
n1 = PadZeroToLeft(n1, length2 - length1);
n2 = PadZeroToLeft(n2, length1 - length2);
var sum = new PartialSum();
var partialSum = RecAdd(sum, n1, n2);
Node resultHead = partialSum.Sum;
if (partialSum.Carry > 0)
{
// Insert before
var newHead = new Node(partialSum.Carry);
newHead.Next = resultHead;
resultHead = newHead;
}
return(resultHead);
}
private static PartialSum RecAdd(PartialSum sum, Node n, Node m)
{
if (n == null && m == null)
{
return(sum);
}
var sum2 = RecAdd(sum, n.Next, m.Next);
var val = n.Value + m.Value + sum2.Carry;
var newNode = new Node(val % 10);
newNode.Next = sum2.Sum;
sum2.Sum = newNode;
sum2.Carry = val / 10;
return(sum2);
}