add missing file

Author: fredrikluo

misc.go

@@ -0,0 +1,10 @@
+package leaves
+
+func GetNLeaves(trees []lgTree) []int {
+	result := make([]int, len(trees))
+	for idx, tree := range trees {
+		result[idx] = tree.nLeaves()
+	}
+
+	return result
+}