What is the complexity of these Dictionary methods?

Question

Can anyone explain what is the complexity of the following Dictionary methods?

ContainsKey(key)
Add(key,value);

I'm trying to figure out the complexity of a method I wrote:

public void DistinctWords(String s)
{
    Dictionary<string,string> d = new Dictionary<string,string>();
    String[] splitted = s.split(" ");
    foreach ( String ss in splitted)
    { 
        if (!d.containskey(ss))
            d.add(ss,null);
    } 
}

I assumed that the 2 dictionary methods are of log(n) complexity where n is the number of keys in the dictionary. Is this correct?

Answer 1

It's written in the documentation for Dictionary...

The Dictionary generic class provides a mapping from a set of keys to a set of values. Each addition to the dictionary consists of a value and its associated key. Retrieving a value by using its key is very fast, close to O(1), because the Dictionary class is implemented as a hash table.

And for the Add function:

If Count is less than the capacity, this method approaches an O(1) operation. If the capacity must be increased to accommodate the new element, this method becomes an O(n) operation, where n is Count.