autopilot: add Median method

autopilot/graph.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"math/big"
 	"net"
+	"sort"
 	"sync/atomic"
 	"time"
 
@@ -501,3 +502,22 @@ func (m memNode) ForEachChannel(cb func(ChannelEdge) error) error {
 
 	return nil
 }
+
+// Median returns the median value in the slice of Amounts.
+func Median(vals []btcutil.Amount) btcutil.Amount {
+	sort.Slice(vals, func(i, j int) bool {
+		return vals[i] < vals[j]
+	})
+
+	num := len(vals)
+	switch {
+	case num == 0:
+		return 0
+
+	case num%2 == 0:
+		return (vals[num/2-1] + vals[num/2]) / 2
+
+	default:
+		return vals[num/2]
+	}
+}

autopilot/graph_test.go

@@ -0,0 +1,50 @@
+package autopilot_test
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcutil"
+	"github.com/lightningnetwork/lnd/autopilot"
+)
+
+// TestMedian tests the Median method.
+func TestMedian(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		values []btcutil.Amount
+		median btcutil.Amount
+	}{
+		{
+			values: []btcutil.Amount{},
+			median: 0,
+		},
+		{
+			values: []btcutil.Amount{10},
+			median: 10,
+		},
+		{
+			values: []btcutil.Amount{10, 20},
+			median: 15,
+		},
+		{
+			values: []btcutil.Amount{10, 20, 30},
+			median: 20,
+		},
+		{
+			values: []btcutil.Amount{30, 10, 20},
+			median: 20,
+		},
+		{
+			values: []btcutil.Amount{10, 10, 10, 10, 5000000},
+			median: 10,
+		},
+	}
+
+	for _, test := range testCases {
+		res := autopilot.Median(test.values)
+		if res != test.median {
+			t.Fatalf("expected median %v, got %v", test.median, res)
+		}
+	}
+}