add kruskal mst

README.md

@@ -68,10 +68,10 @@ Try to keep the interface and variable name consistent with the original book wh
     * [Topological](algs4/topological.py)
     * [KosarajuSCC](algs4/kosaraju_scc.py)
   * MST
-    * [EdgeWeightedGraph](cmd/edge_weighted_graph.py)
-    * [LazyPrimMST](cmd/lazy_prim_mst.py)
-    * [PrimMST](cmd/prim_mst.py)
-    * [KruskalMST](cmd/kruskal_mst.py)
+    * [EdgeWeightedGraph](algs4/edge_weighted_graph.py)
+    * [LazyPrimMST](algs4/lazy_prim_mst.py)
+    * [PrimMST](algs4/prim_mst.py)
+    * [KruskalMST](algs4/kruskal_mst.py)
 
 * 5 STRING
 

algs4/edge_weighted_graph.py

@@ -61,7 +61,7 @@ def edges(self):
         for v in range(self.V):
             for e in self.adj[v]:
                 if e.other(v) > v:
-                    edges.append(v)
+                    edges.append(e)
         return edges
 
 

algs4/kruskal_mst.py

@@ -0,0 +1,74 @@
+"""
+ *  Execution:    python kruskal_mst.py filename.txt
+ *  Data files:   https://algs4.cs.princeton.edu/43mst/tinyEWG.txt
+ *                https://algs4.cs.princeton.edu/43mst/mediumEWG.txt
+ *                https://algs4.cs.princeton.edu/43mst/largeEWG.txt
+ *
+ *  Compute a minimum spanning forest using a lazy version of Prim's
+ *  algorithm.
+ *
+ *  %  python kruskal_mst.py tinyEWG.txt
+ *  0-7 0.16000
+ *  1-7 0.19000
+ *  0-2 0.26000
+ *  2-3 0.17000
+ *  5-7 0.28000
+ *  4-5 0.35000
+ *  6-2 0.40000
+ *  1.81000
+ *
+ *  % python kruskal_mst.py mediumEWG.txt
+ *  0-225   0.02383
+ *  49-225  0.03314
+ *  44-49   0.02107
+ *  44-204  0.01774
+ *  49-97   0.03121
+ *  202-204 0.04207
+ *  176-202 0.04299
+ *  176-191 0.02089
+ *  68-176  0.04396
+ *  58-68   0.04795
+ *  10.46351
+ *
+ *  % python kruskal_mst.py largeEWG.txt
+ *  ...
+ *  647.66307
+ *
+"""
+
+from algs4.edge_weighted_graph import EdgeWeightedGraph
+from algs4.min_pq import MinPQ
+from algs4.queue import Queue
+from algs4.uf import UF
+
+
+class KruskalMST:
+    def __init__(self, g):
+        self.weight = 0
+        self.mst = Queue()
+        self.pq = MinPQ()
+        for e in g.edges():
+            self.pq.insert(e)
+
+        uf = UF(g.V)
+        while not self.pq.is_empty() and self.mst.size() < g.V - 1:
+            e = self.pq.del_min()
+            v = e.either()
+            w = e.other(v)
+            if uf.connected(v, w):
+                continue
+            uf.union(v, w)
+            self.mst.enqueue(e)
+            self.weight += e.weight
+
+    def edges(self):
+        return self.mst
+
+
+if __name__ == "__main__":
+    import sys
+    g = EdgeWeightedGraph(file=open(sys.argv[1]))
+    mst = KruskalMST(g)
+    for e in mst.edges():
+        print(e)
+    print("%.5f" % mst.weight)

algs4/prim_mst.py

@@ -38,7 +38,6 @@
 
 from algs4.edge_weighted_graph import EdgeWeightedGraph
 from algs4.index_min_pq import IndexMinPQ
-from algs4.queue import Queue
 
 
 class PrimMST: