/// <summary>
/// Looks for valid (according given parity) numbers and tries to link them with already found numbers in previous line
/// </summary>
/// <param name="lineNumber">Denotes current line number (also servses as a count of numbers in the line)</param>
/// <param name="validParity">Parity that numbers have to match</param>
/// <param name="previousLineNumbers">valid numbers from previous line</param>
/// <returns></returns>
private List <LineNumber> FindNumbersInLine(int lineNumber, Parity validParity, List <LineNumber> previousLineNumbers)
{
var iterator = new LineIterator(previousLineNumbers);
var expectedCount = 2 * previousLineNumbers.Count;
var pathEndings = new List <LineNumber>(expectedCount > lineNumber ? lineNumber : expectedCount);
var itemIndex = 0;
LineNumber related;
do
{
// read a number from the input
var number = _numbers.Current;
// validate the number and try to link to one from previous line
if (number.GetParity() == validParity && TryFindRelatedNumber(itemIndex, ref iterator, out related))
{
pathEndings.Add(new LineNumber(itemIndex, number, related));
}
// when all numbers of a line are traversed, we return sub-result
if (++itemIndex == lineNumber)
{
return(pathEndings);
}
}while (_numbers.MoveNext());
// error: the line does not contain a proper count of numbers
throw new ArgumentException("Input doesn't contain all the numbers to complete the task!");
}
/// <summary>
/// Searches for related number in previous line by given index of a number in current line
/// </summary>
/// <remarks>
/// Line j-1: N(i-1) N(i)
/// Line j : N(i)
///
/// here N(k) denotes some number with index k,
///
/// a number N(i) from line j IS in relation only with a number N(i-1) or N(i) from line j-1,
/// (a number N(0) as well as N(j) has only one relation, all other have two relations)
/// </remarks>
/// <returns>True, if was able to locate such number</returns>
private bool TryFindRelatedNumber(int itemIndex, ref LineIterator iterator, out LineNumber related)
{
related = null;
if (!iterator.CanIterate)
{
return(false);
}
do
{
// take a number from previous line, that is not yet linked
var current = iterator.Current;
var currentIndex = current.Index;
if (itemIndex < currentIndex)
{
return(false);
}
if (itemIndex - 1 == currentIndex)
{
// case when for a number N(i) in line j (i == itemIndex)
// found number N(i-1) in line j-1
related = iterator.Next;
// before return we need to check, if N(i) in line j-1 is also selected as valid;
// if both exists, then we choose for relation one, having bigger subtotal
var isNextRelated =
related != null &&
related.Index == itemIndex &&
related.SubTotal >= current.SubTotal;
if (!isNextRelated)
{
related = current;
}
return(true);
}
if (itemIndex == currentIndex)
{
// case when for a number N(i) in line j (i == itemIndex)
// found number N(i) in line j-1,
// and if we are here, than N(i-1) is not selected as valid
related = current;
return(true);
}
} while (iterator.MoveNext());
return(false);
}
