Depth First Search - artificial intelligence:

Depth first search is very similar to breadth first, except for that the things are added to the top of this agenda rather than of the bottom. In our example we can notice, the first three things on the agenda would still be: 

Conversely, once the 'D' state has been found, the actions for this:  

1.(empty,add'D')

2.(empty,add'N')

3. (empty,add 'A')

They would be added to the top of the agenda for a certain reason, so it would look like this: 

4. ('D',add 'D')

5. ('D',add 'N')

6. ('D',add 'A')

 Obviously, carrying out this action at the top of the agenda and would introduce the string 'DD', but this would cause the action for: 

('DD',add 'D')

 Add to the top, and the next string found would be 'DDD'. Undoubtedly this can't go on indefinitely, and in the practice, we must have to specify a depth limit to stop for going down a particular path forever. Because is, our agent will need to record how far down a particular path it has been gone, and have to avoid putting actions on the agenda if there is the state in the agenda item that is past a certain depth.