[Test] Revise benchmarks for Fibonacci heap

fibheap/benchmarks.txt

@@ -1,7 +1,8 @@
-BenchmarkFibHeap_Enqueue-4       	10000000	       167 ns/op	      72 B/op	       1 allocs/op
-BenchmarkFibHeap_DequeueMin-4    	   20000	    229153 ns/op	  167035 B/op	       2 allocs/op
-BenchmarkFibHeap_DecreaseKey-4   	10000000	       105 ns/op	      80 B/op	       1 allocs/op
-BenchmarkFibHeap_Delete-4        	   10000	    109693 ns/op	   85836 B/op	       2 allocs/op
-BenchmarkFibHeap_Merge-4         	 5000000	       268 ns/op	     144 B/op	       3 allocs/op
+BenchmarkFibHeap_Enqueue-4       	10000000	       280 ns/op	      64 B/op	       1 allocs/op
+BenchmarkFibHeap_DequeueMin-4    	     100	  16990302 ns/op	16007168 B/op	       2 allocs/op
+BenchmarkFibHeap_DecreaseKey-4   	20000000	       900 ns/op	     122 B/op	       3 allocs/op
+BenchmarkFibHeap_Delete-4        	     100	  19087592 ns/op	16007168 B/op	       2 allocs/op
+BenchmarkFibHeap_Merge-4         	 3000000	       482 ns/op	     128 B/op	       2 allocs/op
 PASS
-ok  	_/home/nikola/git/go-datastructures/fibheap	11.457s
+coverage: 96.2% of statements
+ok  	_/home/nikola/git/go-datastructures/fibheap	37.206s

fibheap/fibheap_test.go

@@ -362,23 +362,19 @@ func BenchmarkFibHeap_Enqueue(b *testing.B) {
 
 	heap := NewFloatFibHeap()
 
-	slice := make([]float64, 0, b.N)
 	for i := 0; i < b.N; i++ {
-		slice = append(slice, 2*1E10*(rand.Float64()-0.5))
-	}
-
-	for i := 0; i < b.N; i++ {
-		heap.Enqueue(slice[i])
+		heap.Enqueue(2 * 1E10 * (rand.Float64() - 0.5))
 	}
 }
 
 // Runs in O(log(N)) time
 func BenchmarkFibHeap_DequeueMin(b *testing.B) {
 
 	heap := NewFloatFibHeap()
+	N := 1000000
 
-	slice := make([]float64, 0, b.N)
-	for i := 0; i < b.N; i++ {
+	slice := make([]float64, 0, N)
+	for i := 0; i < N; i++ {
 		slice = append(slice, 2*1E10*(rand.Float64()-0.5))
 		heap.Enqueue(slice[i])
 	}
@@ -392,27 +388,35 @@ func BenchmarkFibHeap_DequeueMin(b *testing.B) {
 // Runs in O(1) amortized time
 func BenchmarkFibHeap_DecreaseKey(b *testing.B) {
 	heap := NewFloatFibHeap()
+	N := 10000000
 
-	sliceFlt := make([]float64, 0, b.N)
-	sliceE := make([]*Entry, 0, b.N)
-	for i := 0; i < b.N; i++ {
+	sliceFlt := make([]float64, 0, N)
+	sliceE := make([]*Entry, 0, N)
+	for i := 0; i < N; i++ {
 		sliceFlt = append(sliceFlt, 2*1E10*(float64(i)-0.5))
 		sliceE = append(sliceE, heap.Enqueue(sliceFlt[i]))
 	}
 
+	b.ResetTimer()
+	offset := float64(2)
 	for i := 0; i < b.N; i++ {
+		// Change offset if b.N larger than N
+		if i%N == 0 && i > 0 {
+			offset *= float64(i / N)
+		}
 		// Shift-decrease keys
-		heap.DecreaseKey(sliceE[i], sliceFlt[i]-2E10)
+		heap.DecreaseKey(sliceE[i%N], sliceFlt[i%N]-offset)
 	}
 }
 
 // Runs in O(log(N)) time
 func BenchmarkFibHeap_Delete(b *testing.B) {
 	heap := NewFloatFibHeap()
+	N := 1000000
 
-	sliceFlt := make([]float64, 0, b.N)
-	sliceE := make([]*Entry, 0, b.N)
-	for i := 0; i < b.N; i++ {
+	sliceFlt := make([]float64, 0, N)
+	sliceE := make([]*Entry, 0, N)
+	for i := 0; i < N; i++ {
 		sliceFlt = append(sliceFlt, 2*1E10*(float64(i)-0.5))
 		sliceE = append(sliceE, heap.Enqueue(sliceFlt[i]))
 	}