[WIP] ENH: add support for all types of problems in Bidirectional Search (aimacode#1147)

* ENH: all problems can now use BS

* TST: add test for all types of problems for BS

Author: tirthasheshpatel

search.py

@@ -327,9 +327,11 @@ def iterative_deepening_search(problem):
 # Pseudocode from https://webdocs.cs.ualberta.ca/%7Eholte/Publications/MM-AAAI2016.pdf
 
 def bidirectional_search(problem):
-    e = problem.find_min_edge()
-    gF, gB = {problem.initial: 0}, {problem.goal: 0}
-    openF, openB = [problem.initial], [problem.goal]
+    e = 0
+    if isinstance(problem, GraphProblem):
+        e = problem.find_min_edge()
+    gF, gB = {Node(problem.initial): 0}, {Node(problem.goal): 0}
+    openF, openB = [Node(problem.initial)], [Node(problem.goal)]
     closedF, closedB = [], []
     U = np.inf
 
@@ -340,14 +342,14 @@ def extend(U, open_dir, open_other, g_dir, g_other, closed_dir):
         open_dir.remove(n)
         closed_dir.append(n)
 
-        for c in problem.actions(n):
+        for c in n.expand(problem):
             if c in open_dir or c in closed_dir:
-                if g_dir[c] <= problem.path_cost(g_dir[n], n, None, c):
+                if g_dir[c] <= problem.path_cost(g_dir[n], n.state, None, c.state):
                     continue
 
                 open_dir.remove(c)
 
-            g_dir[c] = problem.path_cost(g_dir[n], n, None, c)
+            g_dir[c] = problem.path_cost(g_dir[n], n.state, None, c.state)
             open_dir.append(c)
 
             if c in open_other:
@@ -372,15 +374,15 @@ def find_key(pr_min, open_dir, g):
         """Finds key in open_dir with value equal to pr_min
         and minimum g value."""
         m = np.inf
-        state = -1
+        node = Node(-1)
         for n in open_dir:
             pr = max(g[n] + problem.h(n), 2 * g[n])
             if pr == pr_min:
                 if g[n] < m:
                     m = g[n]
-                    state = n
+                    node = n
 
-        return state
+        return node
 
     while openF and openB:
         pr_min_f, f_min_f, g_min_f = find_min(openF, gF)

tests/test_search.py

@@ -71,6 +71,8 @@ def test_depth_limited_search():
 
 def test_bidirectional_search():
     assert bidirectional_search(romania_problem) == 418
+    assert bidirectional_search(eight_puzzle) == 12
+    assert bidirectional_search(EightPuzzle((1, 2, 3, 4, 5, 6, 0, 7, 8))) == 2
 
 
 def test_astar_search():