Merge pull request aimacode#117 from reachtarunhere/onlinedfs

norvig · norvig · commit bb249b5ee810 · 2016-03-11T12:16:08.000-08:00
Implemented Online DFS Agent
diff --git a/search.py b/search.py
@@ -402,9 +402,49 @@ def and_search(states, problem, path):
     return or_search(problem.initial, problem, [])
 
 
-def online_dfs_agent(s1):
-    "[Fig. 4.21]"
-    unimplemented()
+class OnlineDFSAgent:
+
+    """The abstract class for an OnlineDFSAgent. Override update_state
+    method to convert percept to state. While initilizing the subclass
+    a problem needs to be provided which is an instance of a subclass
+    of the Problem Class. [Fig. 4.21] """
+
+    def __init__(self, problem):
+        self.problem = problem
+        self.s = None
+        self.a = None
+        self.untried = defaultdict(list)
+        self.unbacktracked = defaultdict(list)
+        self.result = {}
+
+    def update_state(self, percept):
+        raise NotImplementedError
+
+    def run(self, percept):
+        current_state = self.update_state(percept)
+        if self.problem.goal_test(current_state):
+            self.a = None
+        else:
+            if current_state not in self.untried.keys():
+                self.untried[current_state] = self.problem.actions(current_state)
+            if self.s is not None:
+                if current_state != self.result[(self.s, self.a)]:
+                    self.result[(self.s, self.a)] = current_state
+                    unbacktracked[current_state].insert(0, self.s)
+            if len(self.untried[current_state]) == 0:
+                if len(self.unbacktracked[current_state]) == 0:
+                    self.a = None
+                else:
+                    # else a <- an action b such that result[s', b] = POP(unbacktracked[s'])
+                    unbacktracked_pop = self.unbacktracked[current_state].pop(0)
+                    for (s,b) in self.result.keys():
+                        if self.result[(s,b)] == unbacktracked_pop:
+                            self.a = b
+                            break
+            else:
+                self.a = self.untried[current_state].pop(0)
+        self.s = current_state
+        return self.a
 
 
 def lrta_star_agent(s1):
