新增排行榜服务

util/algorithms/skip/iterator.go

@@ -0,0 +1,86 @@
+/*
+Copyright 2014 Workiva, LLC
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package skip
+
+const iteratorExhausted = -2
+
+// iterator represents an object that can be iterated.  It will
+// return false on Next and nil on Value if there are no further
+// values to be iterated.
+type iterator struct {
+	first bool
+	n     *node
+}
+
+// Next returns a bool indicating if there are any further values
+// in this iterator.
+func (iter *iterator) Next() bool {
+	if iter.first {
+		iter.first = false
+		return iter.n != nil
+	}
+
+	if iter.n == nil {
+		return false
+	}
+
+	iter.n = iter.n.forward[0]
+	return iter.n != nil
+}
+
+// Prev returns a bool indicating if there are any Previous values
+// in this iterator.
+func (iter *iterator) Prev() bool {
+	if iter.first {
+		iter.first = false
+		return iter.n != nil
+	}
+
+	if iter.n == nil {
+		return false
+	}
+
+	iter.n = iter.n.preNode
+	return iter.n != nil && iter.n.entry != nil
+}
+
+// Value returns a Comparator representing the iterator's present
+// position in the query.  Returns nil if no values remain to iterate.
+func (iter *iterator) Value() Comparator {
+	if iter.n == nil {
+		return nil
+	}
+
+	return iter.n.entry
+}
+
+// exhaust is a helper method to exhaust this iterator and return
+// all remaining entries.
+func (iter *iterator) exhaust() Comparators {
+	entries := make(Comparators, 0, 10)
+	for i := iter; i.Next(); {
+		entries = append(entries, i.Value())
+	}
+
+	return entries
+}
+
+// nilIterator returns an iterator that will always return false
+// for Next and nil for Value.
+func nilIterator() *iterator {
+	return &iterator{}
+}