MST memory improvement

Author: rschio

mst.go

@@ -19,16 +19,18 @@ func MST(g Iterator) (parent []int) {
 
 	// Prim's algorithm
 	Q := newPrioQueue(cost)
+	var v int
+	do := func(w int, c int64) (skip bool) {
+		if Q.Contains(w) && c < cost[w] {
+			cost[w] = c
+			Q.Fix(w)
+			parent[w] = v
+		}
+		return
+	}
 	for Q.Len() > 0 {
-		v := Q.Pop()
-		g.Visit(v, func(w int, c int64) (skip bool) {
-			if Q.Contains(w) && c < cost[w] {
-				cost[w] = c
-				Q.Fix(w)
-				parent[w] = v
-			}
-			return
-		})
+		v = Q.Pop()
+		g.Visit(v, do)
 	}
 	return
 }

mst_test.go

@@ -34,6 +34,7 @@ func TestMST(t *testing.T) {
 
 func BenchmarkMST(b *testing.B) {
 	n := 1000
+	b.ReportAllocs()
 	b.StopTimer()
 	g := New(n)
 	for i := 0; i < 2*n; i++ {

testdata/bench_after/MST

@@ -0,0 +1,7 @@
+goos: linux
+goarch: amd64
+pkg: github.com/rschio/graph
+cpu: Intel(R) Core(TM) i5-8350U CPU @ 1.70GHz
+BenchmarkMST-8   	    5379	    189717 ns/op	   32951 B/op	       8 allocs/op
+PASS
+ok  	github.com/rschio/graph	1.048s

testdata/bench_before/MST

@@ -0,0 +1,7 @@
+goos: linux
+goarch: amd64
+pkg: github.com/rschio/graph
+cpu: Intel(R) Core(TM) i5-8350U CPU @ 1.70GHz
+BenchmarkMST-8   	    4191	    249128 ns/op	   96883 B/op	    1006 allocs/op
+PASS
+ok  	github.com/rschio/graph	1.078s

testdata/bench_results/MST

@@ -0,0 +1,8 @@
+name   old time/op    new time/op    delta
+MST-8     249µs ± 0%     190µs ± 0%  -23.85%
+
+name   old alloc/op   new alloc/op   delta
+MST-8    96.9kB ± 0%    33.0kB ± 0%  -65.99%
+
+name   old allocs/op  new allocs/op  delta
+MST-8     1.01k ± 0%     0.01k ± 0%  -99.20%