projectnetwork.go

@@ -70,7 +70,13 @@ func (g *projectNetwork) forwardPass(toposort []*activity) {
 // backwardPass computes the late times and slack for each activity using the
 // early times
 func (g *projectNetwork) backwardPass(toposort []*activity) {
-	for i := len(toposort) - 1; i >= 0; i-- {
+	n := len(toposort)
+
+	end := toposort[n-1]
+	end.lateFinish = end.earlyFinish
+	end.lateStart = end.lateFinish - end.duration
+
+	for i := n - 2; i >= 0; i-- {
 		a := toposort[i]
 		g.setLateTimes(a)
 	}
@@ -78,30 +84,25 @@ func (g *projectNetwork) backwardPass(toposort []*activity) {
 
 // setEarlyTimes sets the early times for an activity
 func (g *projectNetwork) setEarlyTimes(a *activity) {
+	es := 0.0
 	predecessors := g.To(a.ID())
 	for predecessors.Next() {
 		p := predecessors.Node().(*activity)
-		if a.earlyStart < p.earlyFinish {
+		es = math.Max(es, p.earlyFinish)
-			a.earlyStart = p.earlyFinish
-		}
 	}
+	a.earlyStart = es
 	a.earlyFinish = a.earlyStart + a.duration
 }
 
 // setLateTimes sets the late times for an activity
 func (g *projectNetwork) setLateTimes(a *activity) {
-	a.lateFinish = math.Inf(1)
+	lf := math.Inf(1)
 	successors := g.From(a.ID())
 	for successors.Next() {
 		s := successors.Node().(*activity)
-		if a.lateFinish > s.lateStart {
+		lf = math.Min(lf, s.lateStart)
-			a.lateFinish = s.lateStart
-		}
-	}
-
-	if a.lateFinish == math.Inf(1) {
-		a.lateFinish = a.earlyFinish
 	}
+	a.lateFinish = lf
 	a.lateStart = a.lateFinish - a.duration
 	a.slack = a.lateFinish - a.earlyFinish
 }