Solve problem 81 to 83 in Python and learn A* algorithm along the way.

python/lib_a_star.py

@@ -0,0 +1,33 @@
+class A_Star(object):
+    def __init__(self, starts, goals, h, d, neighbors):
+        """
+        :param h: heuristic function
+        :param d: cost from node to node function
+        :param neighbors: neighbors function
+        """
+        open_set = []
+        g_score = {}
+        f_score = {}
+
+        for start in starts:
+            open_set.append(start)
+            g_score[start] = d(0, start)
+            f_score[start] = h(start)
+
+        while open_set:
+            open_set.sort(key=lambda node: f_score[node])
+            current = open_set[0]
+
+            if current in goals:
+                self.cost = g_score[current]
+                break
+
+            open_set = open_set[1:]  # remove current
+
+            for neighbor in neighbors(current):
+                tentative_g_score = g_score[current] + d(current, neighbor)
+                if neighbor not in g_score or \
+                   tentative_g_score < g_score[neighbor]:
+                    g_score[neighbor] = tentative_g_score
+                    f_score[neighbor] = g_score[neighbor] + h(neighbor)
+                    open_set.append(neighbor)