day25: wow, part 1

day25/example-after-removing.mmd

@@ -1,15 +1,15 @@
-flowchart LR
-	bvb --- cmg
-	hfx --- ntq
-	frs --- lsr
+flowchart TD
+	cmg --- qnr
+	cmg --- lhk
 	jqt --- nvd
-	lhk --- lsr
-	bvb --- ntq
 	bvb --- rhn
-	bvb --- xhk
-	frs --- rsh
-	pzl --- rsh
-	jqt --- ntq
-	lhk --- nvd
+	lsr --- pzl
+	lhk --- lsr
+	lsr --- rsh
+	hfx --- ntq
 	qnr --- rzs
-	cmg --- rzs
+	bvb --- hfx
+	lhk --- nvd
+	frs --- qnr
+	jqt --- ntq
+	rhn --- xhk

day25/example-before-removing.mmd

@@ -1,34 +1,34 @@
 flowchart TD
+	ntq --- xhk
+	bvb --- hfx
 	lsr --- pzl
-	nvd --- qnr
-	lhk --- lsr
 	nvd --- pzl
-	rhn --- xhk
-	jqt --- rhn
-	cmg --- lhk
+	pzl --- rsh
+	frs --- lhk
 	bvb --- cmg
 	jqt --- xhk
-	frs --- lsr
-	lsr --- rsh
-	hfx --- pzl
-	hfx --- xhk
-	frs --- lhk
-	pzl --- rsh
-	jqt --- ntq
-	hfx --- ntq
-	lhk --- nvd
-	lsr --- rzs
-	bvb --- xhk
-	frs --- rsh
-	qnr --- rzs
 	bvb --- rhn
-	bvb --- hfx
+	jqt --- rhn
+	hfx --- xhk
+	frs --- lsr
+	lhk --- lsr
 	jqt --- nvd
 	cmg --- rzs
-	cmg --- nvd
-	bvb --- ntq
-	ntq --- xhk
-	frs --- qnr
-	rsh --- rzs
-	hfx --- rhn
+	hfx --- pzl
+	bvb --- xhk
+	rhn --- xhk
+	frs --- rsh
 	cmg --- qnr
+	nvd --- qnr
+	qnr --- rzs
+	bvb --- ntq
+	frs --- qnr
+	cmg --- nvd
+	hfx --- rhn
+	jqt --- ntq
+	hfx --- ntq
+	lsr --- rsh
+	cmg --- lhk
+	rsh --- rzs
+	lhk --- nvd
+	lsr --- rzs

day25/graph.go

@@ -68,8 +68,9 @@ func (g *Graph) readGraphLine(l string)  {
 	return
 }
 
+// NOTE this is so sad. nodeA.Neighbors.Remove(nodeB.Name) hangs for a reason i don't understand
 func (g *Graph) RemoveEdge(a, b string) {
-	log.Printf("entering remove edge for %s and %s", a, b)
+	// log.Printf("entering remove edge for %s and %s", a, b)
 	nodeA, existsA := g.Nodes[a]
 	// log.Println("got first node", nodeA, existsA)
 	nodeB, existsB := g.Nodes[b]
@@ -79,52 +80,52 @@ func (g *Graph) RemoveEdge(a, b string) {
 	}
 
 	// log.Println("before removals")
-	newANeighbors := mapset.NewSet[string]()
-	for oldNeighbor := range nodeA.Neighbors.Iter() {
-		if oldNeighbor != nodeB.Name {
-			newANeighbors.Add(oldNeighbor)
-		}
-	}
-	log.Println("before remove first", nodeA)
-	nodeA.Neighbors = newANeighbors
+	// log.Println("before remove first", nodeA)
+	// nodeA.Neighbors = newANeighbors
+	nodeA.Neighbors = nodeA.Neighbors.Difference(mapset.NewSet[string](nodeB.Name))
 	// nodeA.Neighbors.Remove(nodeB.Name)
-	log.Println("removed first", nodeA)
+	// log.Println("removed first", nodeA)
 
-	newBNeighbors := mapset.NewSet[string]()
-	for oldNeighbor := range nodeB.Neighbors.Iter() {
-		if oldNeighbor != nodeA.Name {
-			newBNeighbors.Add(oldNeighbor)
-		}
-	}
-	log.Println("before remove second", nodeB)
-	nodeB.Neighbors = newBNeighbors
+	// log.Println("before remove second", nodeB)
+	// nodeB.Neighbors = newBNeighbors
+	nodeB.Neighbors = nodeB.Neighbors.Difference(mapset.NewSet[string](nodeA.Name))
 	// nodeB.Neighbors.Remove(nodeA.Name)
-	log.Println("removed second", nodeB)
+	// log.Println("removed second", nodeB)
+}
+
+func (g *Graph) AddEdge(a, b string) {
+	nodeA, existsA := g.Nodes[a]
+	nodeB, existsB := g.Nodes[b]
+	if !existsA || !existsB {
+		panic("requesting not found node")
+	}
+	nodeA.Neighbors.Add(nodeB.Name)
+	nodeB.Neighbors.Add(nodeA.Name)
 }
 
 func (g *Graph) findCycle() (from, to string, exists bool) {
-	log.Printf(">>>> starting new find cycle")
+	// log.Printf(">>>> starting new find cycle")
 	var firstNode *Node
 	for _, n := range g.Nodes {
 		firstNode = n
 		break
 	}
-	log.Printf("initial search from %s and neighbors %+v", firstNode.Name, firstNode.Neighbors)
+	// log.Printf("initial search from %s and neighbors %+v", firstNode.Name, firstNode.Neighbors)
 	for neighborName := range firstNode.Neighbors.Iter() {
 		initialVisited := mapset.NewSet[string](firstNode.Name)
-		log.Printf("initial dfs from %s to %s with initial visited %+v", firstNode.Name, neighborName, initialVisited)
+		// log.Printf("initial dfs from %s to %s with initial visited %+v", firstNode.Name, neighborName, initialVisited)
 		from, to, exists = g.dfcCycle(firstNode.Name, neighborName, initialVisited)
 		if exists {
 			break
 		}
 	}
 
-	log.Printf("<<<< cycle %t, from %s to %s", exists, from, to)
+	// log.Printf("<<<< cycle %t, from %s to %s", exists, from, to)
 	return
 }
 
 func (g *Graph) dfcCycle(fromName, atName string, visited mapset.Set[string]) (cycleFrom, cycleTo string, cycleExists bool) {
-	log.Printf("> step from %+v to %+v. visited : %+v", fromName, atName, visited)
+	// log.Printf("> step from %+v to %+v. visited : %+v", fromName, atName, visited)
 	if visited.Cardinality() == len(g.Nodes) {
 		log.Println("exit by visited all")
 		return
@@ -215,6 +216,9 @@ func (g *Graph)SaveAsMermaid(filename string) {
 type Edge struct {
 	smaller, bigger string
 }
+func (e Edge)String() string {
+	return fmt.Sprintf("%s/%s", e.smaller, e.bigger)
+}
 
 func CreateEdge(a, b string) Edge {
 	var smaller, bigger string
@@ -235,7 +239,7 @@ func (g *Graph) RemoveAllCycles() (removedEdges mapset.Set[Edge]) {
 	for hasCycle {
 		from, to, hasCycle = g.findCycle()
 		if hasCycle {
-			log.Printf("\n!!!! found cycle %s to %s\n", from, to)
+			// log.Printf("\n!!!! found cycle %s to %s\n", from, to)
 			edgeToRemove := CreateEdge(from, to)
 			removedEdges.Add(edgeToRemove)
 			g.RemoveEdge(from, to)
@@ -243,3 +247,55 @@ func (g *Graph) RemoveAllCycles() (removedEdges mapset.Set[Edge]) {
 	}
 	return
 }
+
+func (g *Graph) TryToSplit() (componentSizeMult int) {
+	// first remove all cycles
+	removedEdges := g.RemoveAllCycles()
+	g.SaveAsMermaid("after-removing-cycles.mmd")
+	// log.Printf("all removed edges %+v, two of them are necessary to split initial graph into 2 ", removedEdges)
+
+	triedEdges := mapset.NewSet[Edge]()
+
+	for _, node := range g.Nodes {
+		for neighborName := range node.Neighbors.Iter() {
+			edge := CreateEdge(neighborName, node.Name)
+			if triedEdges.Contains(edge) {
+				continue
+			}
+			triedEdges.Add(edge)
+			// first remove the edge
+			g.RemoveEdge(edge.bigger, edge.smaller)
+
+			// then ask for components of the nodes of removed edge
+			compA := g.ComponentFrom(edge.bigger)
+			compB := g.ComponentFrom(edge.smaller)
+
+			// iterate over the initially removed edges. only two of them should be 'connecting'
+			// i.e were necessary to remove
+			necessaryEdgesCount := 0
+			for initiallyRemovedEdge := range removedEdges.Iter() {
+				endA, endB := initiallyRemovedEdge.bigger, initiallyRemovedEdge.smaller
+				isNonNecessary := (compA.Contains(endA) && compA.Contains(endB)) || (compB.Contains(endA) && compB.Contains(endB))
+				if !isNonNecessary {
+					// log.Printf("with edge %+v test removed, the %+v also seems necessary", edge, initiallyRemovedEdge)
+					necessaryEdgesCount += 1
+				}
+			}
+			// log.Printf("with edge %+v test removed neessary count is %d", edge, necessaryEdgesCount)
+
+			// if we found 2 necessary, then our currently tried edge is the third necesary to remove
+			// and out two components are the searched
+			if necessaryEdgesCount == 2 {
+				return compA.Cardinality() * compB.Cardinality()
+			}
+
+			// in the end add edge back if not fitting
+			g.AddEdge(edge.bigger, edge.smaller)
+		}
+	}
+
+	// now huh. if we didn't find `necessaryEdgesCount == 2`
+	// that means 0, 1 or 3
+
+	return
+}

day25/graph_test.go

@@ -2,6 +2,8 @@ package day25
 
 import (
 	"testing"
+
+	mapset "github.com/deckarep/golang-set/v2"
 )
 
 func TestReadFileExample(t *testing.T) {
@@ -54,7 +56,41 @@ func TestRemoveAllCycles(t *testing.T) {
 	g.SaveAsMermaid("example-before-removing.mmd")
 	t.Logf("initial graph is %+v", g)
 	edges := g.RemoveAllCycles()
+	expectedNecessary := mapset.NewSet[Edge](
+		CreateEdge("hfx", "pzl"),
+		CreateEdge("bvb", "cmg"),
+		CreateEdge("nvd", "jqt"),
+	)
+
+	intersection := expectedNecessary.Intersect(edges)
+	t.Logf("i expect that exactly two will be in intersection %+v", intersection)
+	if intersection.Cardinality() != 2 {
+		panic("huh?")
+		// ok, this is not what i expected.
+		// this is unstable. but i could run it several times? and hopefully luck out?
+	}
+
 	t.Logf("removed edges %+v", edges)
 	t.Logf("after removal graph is %+v", g)
 	g.SaveAsMermaid("example-after-removing.mmd")
 }
+
+func TestSplittingExample(t *testing.T) {
+	filename := "example"
+	g := ReadGraphFile(filename)
+	result := g.TryToSplit()
+	t.Logf("hopefully same as example answer: %d", result)
+}
+
+func TestSplittingInput(t *testing.T) {
+	// kind of brute force
+	result := 0
+	filename := "input"
+
+	for result == 0 {
+		g := ReadGraphFile(filename)
+		result = g.TryToSplit()
+		t.Logf("hopefully as answer: %d", result)
+	}
+
+}

day25/notes.org

@@ -456,3 +456,25 @@ PASS
 ok  	sunshine.industries/aoc2023/day25	0.003s
 
 #+end_src
+** kind of bruteforce
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 518391
+    graph_test.go:93: hopefully as answer: 0
+    graph_test.go:93: hopefully as answer: 518391
+    graph_test.go:93: hopefully as answer: 0