AIMA.Core.Search.Online.OnlineDFSAgent.execute C# (CSharp) Method

        public override Action execute(Percept psPrime)
        {
            Object sPrime = ptsFunction.getState(psPrime);
            // if GOAL-TEST(s') then return stop
            if (goalTest(sPrime))
            {
                a = NoOpAction.NO_OP;
            }
            else
            {
                // if s' is a new state (not in untried) then untried[s'] <-
                // ACTIONS(s')
                if (!untried.containsKey(sPrime))
                {
                    untried.put(sPrime, actions(sPrime));
                }

                // if s is not null then do
                if (null != s)
                {
                    // Note: If I've already seen the result of this
                    // [s, a] then don't put it back on the unbacktracked
                    // list otherwise you can keep oscillating
                    // between the same states endlessly.
                    if (!(sPrime.Equals(result.get(s, a))))
                    {
                        // result[s, a] <- s'
                        result.put(s, a, sPrime);

                        // Ensure the unbacktracked always has a list for s'
                        if (!unbacktracked.containsKey(sPrime))
                        {
                            unbacktracked.put(sPrime, new List<Object>());
                        }

                        // add s to the front of the unbacktracked[s']
                        unbacktracked.get(sPrime).Add(0, s);
                    }
                }
                // if untried[s'] is empty then
                if (untried.get(sPrime).isEmpty())
                {
                    // if unbacktracked[s'] is empty then return stop
                    if (unbacktracked.get(sPrime).isEmpty())
                    {
                        a = NoOpAction.NO_OP;
                    }
                    else
                    {
                        // else a <- an action b such that result[s', b] =
                        // POP(unbacktracked[s'])
                        Object popped = unbacktracked.get(sPrime).remove(0);
                        foreach (Pair<Object, Action> sa in result.keySet())
                        {
                            if (sa.getFirst().Equals(sPrime)
                                    && result.get(sa).Equals(popped))
                            {
                                a = sa.getSecond();
                                break;
                            }
                        }
                    }
                }
                else
                {
                    // else a <- POP(untried[s'])
                    a = untried.get(sPrime).remove(0);
                }
            }

            if (a.isNoOp())
            {
                // I'm either at the Goal or can't get to it,
                // which in either case I'm finished so just die.
                setAlive(false);
            }

            // s <- s'
            s = sPrime;
            // return a
            return a;
        }