reorg and add code for second edition

10_greedy_algorithms/python/01_set_covering.py

@@ -0,0 +1,31 @@
+# You pass an array in, and it gets converted to a set.
+states_needed = set(["mt", "wa", "or", "id", "nv", "ut", "ca", "az"])
+
+stations = {}
+stations["kone"] = set(["id", "nv", "ut"])
+stations["ktwo"] = set(["wa", "id", "mt"])
+stations["kthree"] = set(["or", "nv", "ca"])
+stations["kfour"] = set(["nv", "ut"])
+stations["kfive"] = set(["ca", "az"])
+
+
+def my_set_covering(states_needed, stations):
+    final_stations = set()
+    #while states_needed is not None: 这个不对，Set()而不是None
+    while states_needed:
+        best_station = None
+        states_covered = set()
+        for station, states_for_station in stations.items():
+            covered = states_needed & states_for_station
+            if len(covered) > len(states_covered) and station not in final_stations:
+                best_station = station
+                states_covered = covered
+        if best_station is not None:
+            states_needed -= states_covered
+            final_stations.add(best_station)
+            stations.pop(best_station)
+        else:
+            return None
+    return final_stations
+
+print(my_set_covering(states_needed, stations))