How do I get previous key from SortedDictionary?

Question

I have dictionary containing key value pairs.

SortedDictionary dictionary=new SortedDictionary();
dictionary.Add(1,33);
diction         


        

Answer 1

You could loop through the dictionary and keep track of values, I guess. Something like this:

public int GetPreviousKey(int currentKey, SortedDictionary dictionary)
{
    int previousKey = int.MinValue;
    foreach(KeyValuePair pair in dictionary)
    {
        if(pair.Key == currentKey)
        {
            if(previousKey == int.MinValue)
            {
                throw new InvalidOperationException("There is no previous key.");
            }
            return previousKey;
        }
        else
        {
            previousKey = pair.Key;
        }
    }
}

However, this is a pretty odd operation to require. The fact that you need it might be pointing at a problem with your design.