Question

I have following structure:

 class Employee
        {
            public long Id { get; set; }

            public long? ParentId { get; set; }

            public Employee(long id, long? parentId)
            {
                Id = id;
                Parent_Id = parentId;
            }
        }

Let’s build some tree structure:

        var employees = new List<Employee>();

        employees.Add(new Employee(1 , null));
        employees.Add(new Employee(2 , 1));
        employees.Add(new Employee(3 , 2));

How to check (using C#) if employee with Id=1 is parent of employee with Id=3 within this list? Tree structure could be much more complicated .

Answer 1

To check if is descendant you can traverse up the tree and see if you find him:

static bool GetIsDescendant(long idChild, long idAncestor, IEnumerable<Employee> employees)
{
    return GetAncestors(idChild, employees).Any(t => t.Id == idAncestor);
}

static IEnumerable<Employee> GetAncestors(long idEmployee, IEnumerable<Employee> employees)
{
    var employee = employees.SingleOrDefault(e => e.Id == idEmployee);

    if (employee == null)
    {
        yield break;
    }

    while (employee.ParentId.HasValue)
    {
        var parent = employees.SingleOrDefault(e => e.Id == employee.ParentId.Value);

        if (parent == null)
        {
            yield break;
        }
        else
        {
            employee = parent;
            yield return parent;
        }
    }
}