graph/simple: factor id handling out of graphs

graph/simple/directed.go

@@ -7,8 +7,6 @@ package simple
 import (
 	"fmt"
 
-	"golang.org/x/tools/container/intsets"
-
 	"gonum.org/v1/gonum/graph"
 )
 
@@ -20,8 +18,7 @@ type DirectedGraph struct {
 
 	self, absent float64
 
-	freeIDs intsets.Sparse
+	nodeIDs idSet
-	usedIDs intsets.Sparse
 }
 
 // NewDirectedGraph returns a DirectedGraph with the specified self and absent
@@ -44,22 +41,9 @@ func (g *DirectedGraph) NewNodeID() int {
 		return 0
 	}
 	if len(g.nodes) == maxInt {
-		panic(fmt.Sprintf("simple: cannot allocate node: no slot"))
+		panic("simple: cannot allocate node: no slot")
 	}
-
+	return g.nodeIDs.newID()
-	var id int
-	if g.freeIDs.Len() != 0 && g.freeIDs.TakeMin(&id) {
-		return id
-	}
-	if id = g.usedIDs.Max(); id < maxInt {
-		return id + 1
-	}
-	for id = 0; id < maxInt; id++ {
-		if !g.usedIDs.Has(id) {
-			return id
-		}
-	}
-	panic("unreachable")
 }
 
 // AddNode adds n to the graph. It panics if the added node ID matches an existing node ID.
@@ -70,9 +54,7 @@ func (g *DirectedGraph) AddNode(n graph.Node) {
 	g.nodes[n.ID()] = n
 	g.from[n.ID()] = make(map[int]graph.Edge)
 	g.to[n.ID()] = make(map[int]graph.Edge)
-
+	g.nodeIDs.use(n.ID())
-	g.freeIDs.Remove(n.ID())
-	g.usedIDs.Insert(n.ID())
 }
 
 // RemoveNode removes n from the graph, as well as any edges attached to it. If the node
@@ -93,8 +75,7 @@ func (g *DirectedGraph) RemoveNode(n graph.Node) {
 	}
 	delete(g.to, n.ID())
 
-	g.freeIDs.Insert(n.ID())
+	g.nodeIDs.release(n.ID())
-	g.usedIDs.Remove(n.ID())
 }
 
 // SetEdge adds e, an edge from one node to another. If the nodes do not exist, they are added.

graph/simple/simple.go

@@ -9,6 +9,8 @@ package simple // import "gonum.org/v1/gonum/graph/simple"
 import (
 	"math"
 
+	"golang.org/x/tools/container/intsets"
+
 	"gonum.org/v1/gonum/graph"
 )
 
@@ -43,3 +45,37 @@ const maxInt int = int(^uint(0) >> 1)
 func isSame(a, b float64) bool {
 	return a == b || (math.IsNaN(a) && math.IsNaN(b))
 }
+
+// idSet implements available ID storage.
+type idSet struct {
+	used, free intsets.Sparse
+}
+
+// newID returns a new unique ID.
+func (s *idSet) newID() int {
+	var id int
+	if s.free.TakeMin(&id) {
+		return id
+	}
+	if id = s.used.Max(); id < maxInt {
+		return id + 1
+	}
+	for id = 0; id < maxInt; id++ {
+		if !s.used.Has(id) {
+			return id
+		}
+	}
+	panic("unreachable")
+}
+
+// use adds the id to the used IDs in the idSet.
+func (s *idSet) use(id int) {
+	s.free.Remove(id)
+	s.used.Insert(id)
+}
+
+// free frees the id for reuse.
+func (s *idSet) release(id int) {
+	s.free.Insert(id)
+	s.used.Remove(id)
+}

graph/simple/undirected.go

@@ -7,8 +7,6 @@ package simple
 import (
 	"fmt"
 
-	"golang.org/x/tools/container/intsets"
-
 	"gonum.org/v1/gonum/graph"
 )
 
@@ -19,8 +17,7 @@ type UndirectedGraph struct {
 
 	self, absent float64
 
-	freeIDs intsets.Sparse
+	nodeIDs idSet
-	usedIDs intsets.Sparse
 }
 
 // NewUndirectedGraph returns an UndirectedGraph with the specified self and absent
@@ -42,22 +39,9 @@ func (g *UndirectedGraph) NewNodeID() int {
 		return 0
 	}
 	if len(g.nodes) == maxInt {
-		panic(fmt.Sprintf("simple: cannot allocate node: no slot"))
+		panic("simple: cannot allocate node: no slot")
 	}
-
+	return g.nodeIDs.newID()
-	var id int
-	if g.freeIDs.Len() != 0 && g.freeIDs.TakeMin(&id) {
-		return id
-	}
-	if id = g.usedIDs.Max(); id < maxInt {
-		return id + 1
-	}
-	for id = 0; id < maxInt; id++ {
-		if !g.usedIDs.Has(id) {
-			return id
-		}
-	}
-	panic("unreachable")
 }
 
 // AddNode adds n to the graph. It panics if the added node ID matches an existing node ID.
@@ -67,9 +51,7 @@ func (g *UndirectedGraph) AddNode(n graph.Node) {
 	}
 	g.nodes[n.ID()] = n
 	g.edges[n.ID()] = make(map[int]graph.Edge)
-
+	g.nodeIDs.use(n.ID())
-	g.freeIDs.Remove(n.ID())
-	g.usedIDs.Insert(n.ID())
 }
 
 // RemoveNode removes n from the graph, as well as any edges attached to it. If the node
@@ -85,9 +67,7 @@ func (g *UndirectedGraph) RemoveNode(n graph.Node) {
 	}
 	delete(g.edges, n.ID())
 
-	g.freeIDs.Insert(n.ID())
+	g.nodeIDs.release(n.ID())
-	g.usedIDs.Remove(n.ID())
-
 }
 
 // SetEdge adds e, an edge from one node to another. If the nodes do not exist, they are added.