private static IEnumerable<IEnumerable<Tuple<int, int>>> GetRoutes(Triangle triangle, Tuple<int,int> startingPosition)
{
var positionsOnNextRow = triangle.GetPositionsOnNextRow(startingPosition).ToList();
if (!positionsOnNextRow.Any())
{
yield return new[] {startingPosition};
yield break;
}
foreach (var nextPosition in positionsOnNextRow)
{
foreach (var route in GetRoutesMemo(triangle, nextPosition))
{
yield return route.Concat(new[] {startingPosition});
}
}
}