issue_765 - fixed bug in Hopcroft-Karp algorithm

Author: timmyb32r

matchers/support/goraph/bipartitegraph/bipartitegraphmatching.go

@@ -4,6 +4,7 @@ import (
 	. "github.com/onsi/gomega/matchers/support/goraph/edge"
 	. "github.com/onsi/gomega/matchers/support/goraph/node"
 	"github.com/onsi/gomega/matchers/support/goraph/util"
+	"slices"
 )
 
 // LargestMatching implements the Hopcroft–Karp algorithm taking as input a bipartite graph
@@ -157,6 +158,11 @@ func (bg *BipartiteGraph) createSLAPGuideLayers(matching EdgeSet) (guideLayers [
 		if len(currentLayer) == 0 {
 			return []NodeOrderedSet{}
 		}
+		if done { // if last layer - into last layer must be only 'free' nodes
+			currentLayer = slices.DeleteFunc(currentLayer, func(in Node)bool{
+				return !matching.Free(in)
+			})
+		}
 		guideLayers = append(guideLayers, currentLayer)
 	}
 

matchers/support/goraph/bipartitegraph/bipartitegraphmatching_test.go

@@ -0,0 +1,91 @@
+package bipartitegraph
+
+import (
+	"github.com/onsi/gomega/matchers/support/goraph/edge"
+	"slices"
+	"testing"
+)
+
+func buildEdgesArr(l, r []interface{}, edges edge.EdgeSet) []string {
+	unpackArr := func(in []interface{}) []string {
+		result := make([]string, 0, len(in))
+		for _, el := range in {
+			result = append(result, el.(string))
+		}
+		return result
+	}
+
+	vertexes := unpackArr(append(l, r...))
+
+	result := make([]string, 0)
+	for _, currEdge := range edges {
+		result = append(result, vertexes[currEdge.Node1]+"-"+vertexes[currEdge.Node2])
+	}
+	return result
+}
+
+func expectedContains(t *testing.T, expected string, edges []string) {
+	idx := slices.IndexFunc(edges, func(c string) bool { return c == expected })
+	if idx == -1 {
+		t.Fatalf("edges %v not contains expected: %s", edges, expected)
+	}
+}
+
+func TestMaximumCardinalityMatch(t *testing.T) {
+	edgesFunc := func(l, r interface{}) (bool, error) {
+		ll := l.(string)
+		rr := r.(string)
+
+		type currEdge struct {
+			l string
+			r string
+		}
+		knownEdges := []currEdge{
+			{"1", "A"},
+			{"1", "B"},
+			{"1", "C"},
+			{"1", "D"},
+			{"1", "E"},
+			{"2", "A"},
+			{"2", "D"},
+			{"3", "B"},
+			{"3", "D"},
+			{"4", "B"},
+			{"4", "D"},
+			{"4", "E"},
+			{"5", "A"},
+		}
+
+		for _, el := range knownEdges {
+			if el.l == ll && el.r == rr {
+				return true, nil
+			}
+		}
+		return false, nil
+	}
+
+	leftPart := []interface{}{"1", "2", "3", "4", "5"}
+	rightPart := []interface{}{"A", "B", "C", "D", "E"}
+
+	bipartiteGraph, err := NewBipartiteGraph(
+		leftPart,
+		rightPart,
+		edgesFunc,
+	)
+	if err != nil {
+		t.Fatalf("NewBipartiteGraph returned error: %v", err)
+	}
+	if err != nil {
+		t.Fatal(err)
+	}
+	edgeSet := bipartiteGraph.LargestMatching()
+	if len(edgeSet) != 5 {
+		t.Fatalf("bipartiteGraph.LargestMatching() returned not 5 elements: %v", edgeSet)
+	}
+	edges := buildEdgesArr(leftPart, rightPart, edgeSet)
+	expectedContains(t, "1-C", edges)
+	expectedContains(t, "2-D", edges)
+	expectedContains(t, "3-B", edges)
+	expectedContains(t, "4-E", edges)
+	expectedContains(t, "5-A", edges)
+}