How to write recursion on loop properly?

Question

I have such List<IRequest>

public interface IRequest
    {
        List<IRequest> Childrens { get; set; }
        bool RequestIsSelected { get; set; }
    }

How to find RequestIsSelected object?

Let's say I have such structure

IRequest -
          |
          IRequest - 
                    |
                     IRequest  <--- if this one is true I can catch it
          |
          IRequest -
                    |
                     IRequest   <----- This one RequestIsSelected == true;  (I can't catch it)

I wrote such method

private IRequest GetSelectedItem(List<IRequest> entireList)
        {
            foreach(var tmp in entireList)
            {
                if(tmp.RequestIsSelected)
                {
                    return tmp;
                }
                else
                {
                    return GetSelectedItem(tmp.Childrens);
                }
            }

            return null;
        }

But it iterates only on first deep line, if my selected item resides in second line my method returns null.

What am I doing wrong?

In the else, only return if the result of the recursive call is not null. — 001
– 001, Commented Oct 2, 2020 at 17:56

001 · Accepted Answer · 2020-10-02 18:00:05Z

1

In the else, only return if the result of the recursive call is not null since not finding it in the current child does not necessarily mean it is not in some other child list.

private IRequest GetSelectedItem(List<IRequest> entireList)
{
    if (entireList == null) return null;

    foreach(var tmp in entireList)
    {
        if(tmp.RequestIsSelected)
        {
            return tmp;
        }
        else
        {
            IRequest child = GetSelectedItem(tmp.Childrens);
            if (child != null) return child; 
            // Else keep searching since it may
            // be in some other child list
        }
    }

    return null;
}

answered Oct 2, 2020 at 18:00

001

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