add kruskal mst

Author: shellfly

README.md

@@ -71,6 +71,7 @@ To test each algorithm(data structure), instead of running the file directly, yo
     * [EdgeWeightedGraph](edge_weighted_graph.go)
     * [LazyPrimMST](lazy_prim_mst.go)
     * [PrimMST](prim_mst.go)
+    * [KruskalMST](kruskal_mst.go)
 
 * 5 STRING
 

cmd/kruskal-mst/main.go

@@ -0,0 +1,56 @@
+/******************************************************************************
+ *  Execution:    go run cmd/kruskal-mst/main.go 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.
+ *
+ *  %  go run cmd/kruskal-mst/main.go 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
+ *
+ *  % go run cmd/kruskal-mst/main.go 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
+ *
+ *  % go run cmd/kruskal-mst/main.go largeEWG.txt
+ *  ...
+ *  647.66307
+ *
+ ******************************************************************************/
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/shellfly/algo"
+	"github.com/shellfly/algo/stdin"
+)
+
+func main() {
+	g := algo.NewEdgeWeightedGraph(stdin.NewIn(os.Args[1]))
+	mst := algo.NewKruskalMST(g)
+	for _, e := range mst.Edges() {
+		fmt.Println(e)
+	}
+	fmt.Printf("%.5f\n", mst.Weight())
+}

cmd/prim-mst/main.go

@@ -45,7 +45,7 @@ import (
 
 func main() {
 	g := algo.NewEdgeWeightedGraph(stdin.NewIn(os.Args[1]))
-	mst := algo.NewLazyPrimMST(g)
+	mst := algo.NewPrimMST(g)
 	for _, e := range mst.Edges() {
 		fmt.Println(e)
 	}

kruskal_mst.go

@@ -0,0 +1,43 @@
+package algo
+
+// KruskalMST ...
+type KruskalMST struct {
+	mst    *Queue
+	weight float32
+}
+
+// NewKruskalMST ...
+func NewKruskalMST(g *EdgeWeightedGraph) *KruskalMST {
+	mst := NewQueue()
+	k := &KruskalMST{mst, 0}
+	pq := NewMinPQ()
+	for _, e := range g.Edges() {
+		pq.Insert(e)
+	}
+	uf := NewUF(g.V())
+	for !pq.IsEmpty() && mst.Size() < g.V()-1 {
+		e := pq.DelMin().(*Edge)
+		v := e.Either()
+		w := e.Other(v)
+		if uf.Connected(v, w) {
+			continue
+		}
+		uf.Union(v, w)
+		k.mst.Enqueue(e)
+		k.weight += e.Weight()
+	}
+	return k
+}
+
+// Weight ...
+func (k *KruskalMST) Weight() float32 {
+	return k.weight
+}
+
+// Edges ...
+func (k *KruskalMST) Edges() (edges []*Edge) {
+	for _, e := range k.mst.Slice() {
+		edges = append(edges, e.(*Edge))
+	}
+	return
+}

prim_mst.go

@@ -64,7 +64,7 @@ func (l *PrimMST) visit(g *EdgeWeightedGraph, v int) {
 		if e.Weight() < l.distTo[w] {
 			l.distTo[w] = e.Weight()
 			l.edgeTo[w] = e
-			if !l.pq.Contains(w) {
+			if l.pq.Contains(w) {
 				l.pq.DecreaseKey(w, FloatPQItem(l.distTo[w]))
 			} else {
 				l.pq.Insert(w, FloatPQItem(l.distTo[w]))