backtracking search

wip

assignment2/csp.py

@@ -130,11 +130,32 @@ class CSP:
             A solution if any exists, otherwise None
         """
 
-        def backtrack(assignment: dict[str, Any]):
-            # YOUR CODE HERE (and remove the assertion below)
-            assert False, "Not implemented"
+        return self._backtrack({})
 
-        return backtrack({})
+    def _select_unassigned_variable(self, assignment) -> str:
+        for v in self.variables:
+            if v not in assignment.keys():
+                return v
+        return "this shouldn't happen"
+
+    # TODO: may be wrong
+    def _order_domain_values(self, var, assignment) -> list[Any]:
+        """least constrained value"""
+
+        def compare(value) -> int:
+            s = 0
+            for neighbor in [
+                b for (a, b) in self.binary_constraints.keys() if a == var
+            ]:
+                if neighbor in assignment.keys():
+                    continue
+                for neighbor_value in self.domains[neighbor]:
+                    s += (value, neighbor_value) not in self.binary_constraints[
+                        (var, neighbor)
+                    ]
+            return s
+
+        return sorted(list(self.domains[var]), key=compare)
 
 
 def alldiff(variables: list[str]) -> list[tuple[str, str]]: