/// <summary>
/// Constructs sub-automaton corresponding to decimal numbers of value between x.Substring(n)
/// and y.Substring(n) and of length x.Substring(n).Length (which must be equal to
/// y.Substring(n).Length).
/// </summary>
/// <param name="x">The x.</param>
/// <param name="y">The y.</param>
/// <param name="n">The n.</param>
/// <param name="initials">The initials.</param>
/// <param name="zeros">if set to <c>true</c> [zeros].</param>
/// <returns></returns>
private static State Between(string x, string y, int n, ICollection <State> initials, bool zeros)
{
var s = new State();
if (x.Length == n)
{
s.Accept = true;
}
else
{
if (zeros)
{
initials.Add(s);
}
char cx = x[n];
char cy = y[n];
if (cx == cy)
{
s.AddTransition(new Transition(cx, Between(x, y, n + 1, initials, zeros && cx == '0')));
}
else
{
// cx < cy
s.AddTransition(new Transition(cx, BasicAutomata.AtLeast(x, n + 1, initials, zeros && cx == '0')));
s.AddTransition(new Transition(cy, BasicAutomata.AtMost(y, n + 1)));
if (cx + 1 < cy)
{
s.AddTransition(new Transition((char)(cx + 1), (char)(cy - 1), BasicAutomata.AnyOfRightLength(x, n + 1)));
}
}
}
return(s);
}