我想使用以下内容在Map中打印一个有序列表:
Map<Float, String> mylist = new HashMap<>();
mylist.put(10.5, a);
mylist.put(12.3, b);
mylist.put(5.1, c);
SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet());
for (Float i : orderlist) {
System.out.println(i+" "+mylist.get(i));
}
以上代码打印:
5.1 c
10.5 a
12.3 b
但是如何以相反的顺序打印订单列表,如下所示:
12.3 b
10.5 a
5.1 c
答案 0 :(得分:6)
如果您愿意以相反的顺序存储city = create(:city)
invalid_city = City.new(country_code: city.country_code, name: city.name)
expect(invalid_city).not_to be_valid
expect(invalid_city.errors.full_messages).to include "This city has already been added"
中的元素,那么您需要进行的唯一更改是使用an appropriate constructor构建SortedSet
,这需要自定义{ {3}}:
TreeSet
注意这里的整洁方法是Comparator
,它返回一个Map<Float, String> mylist = new HashMap<>();
mylist.put(10.5, a);
mylist.put(12.3, b);
mylist.put(5.1, c);
SortedSet<Float> orderlist = new TreeSet<Float>(Collections.reverseOrder());
orderList.addAll(mylist.keySet());
for (Float i : orderlist) {
System.out.println(i+" "+mylist.get(i));
}
,它与元素的自然顺序相反。
答案 1 :(得分:4)
你也可以试试这个:
Map<Float, String> mylist = new HashMap<Float, String>();
mylist.put(10.5, a);
mylist.put(12.3, b);
mylist.put(5.1, c);
SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet()).descendingSet();
for (Float i : orderlist) {
System.out.println(i+" "+mylist.get(i));
}
答案 2 :(得分:2)
尝试使用NavigableSet
:
public NavigableSet<E> descendingSet()
像这样:
SortedSet<Float> orderlist = new TreeSet<Float>(mylist.keySet());
SortedSet<Float> treereverse = new TreeSet<Float>();
// creating reverse set
treereverse=(TreeSet)orderlist.descendingSet();
最后,您的treereverse
顺序相反。
答案 3 :(得分:0)
您可以尝试此实现(source):
public sealed class OrderedSet<T> : ICollection<T>
{
private readonly IDictionary<T, LinkedListNode<T>> _dictionary;
private readonly LinkedList<T> _linkedList;
public OrderedSet()
: this(EqualityComparer<T>.Default)
{
}
private OrderedSet(IEqualityComparer<T> comparer)
{
_dictionary = new Dictionary<T, LinkedListNode<T>>(comparer);
_linkedList = new LinkedList<T>();
}
public int Count => _dictionary.Count;
public bool IsReadOnly => _dictionary.IsReadOnly;
void ICollection<T>.Add(T item)
{
Add(item);
}
public void Clear()
{
_linkedList.Clear();
_dictionary.Clear();
}
public bool Remove(T item)
{
var found = _dictionary.TryGetValue(item, out var node);
if (!found)
{
return false;
}
_dictionary.Remove(item);
_linkedList.Remove(node);
return true;
}
public IEnumerator<T> GetEnumerator()
{
return _linkedList.GetEnumerator();
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
public bool Contains(T item)
{
return _dictionary.ContainsKey(item);
}
public void CopyTo(T[] array, int arrayIndex)
{
_linkedList.CopyTo(array, arrayIndex);
}
public void Add(T item)
{
if (_dictionary.ContainsKey(item))
{
return;
}
var node = _linkedList.AddLast(item);
_dictionary.Add(item, node);
}
public void Reverse()
{
var head = _linkedList.First;
while (head.Next != null)
{
var next = head.Next;
_linkedList.Remove(next);
_linkedList.AddFirst(next.Value);
}
}
}
请注意,这是OrderSet
,它保留插入顺序,而SortedSet
则根据某些比较器(例如,按字母顺序)对集合进行排序。
我从here添加了Reverse()
方法。