LinkedHashMap.put("a.a1","11");
LinkedHashMap.put("a.a12","12");
LinkedHashMap.put("b.b1","13");
LinkedHashMap.put("c.c1","14");
LinkedHashMap.put("c.c1","15");
搜索＆＃34; a。＆＃34; key应返回两个值。
我们应该使用java中的哪个数据结构作为Trie DS实现不可用。我能想到的下一个最好的只是LinkedHashMap
答案 0 :(得分：5)
您正在寻找Apache Patricia Trie。它是您用例的确切数据结构。
来自他们的文档：
PATRICIA Trie是一个压缩的Trie。 PATRICIA不是将所有数据存储在Trie的边缘（并且具有空的内部节点），而是将数据存储在每个节点中。这允许非常有效的遍历，插入，删除，前驱，后继，前缀，范围和选择（对象）操作。所有操作在O（K）时间内最差地执行，其中K是树中最大项目中的位数。实际上，操作实际上需要O（A（K））时间，其中A（K）是树中所有项目的平均位数。
最重要的是，PATRICIA在进行任何操作时都需要很少与键进行比较。在执行查找时，每次比较（最多K个，如上所述）将对给定键执行单个位比较，而不是将整个键与另一个键进行比较。
特别是，prefixMap(prefix) operation会返回一个SortedMap视图，其中包含与给定前缀匹配的所有条目。
再次，来自文档：
例如，如果Trie包含'Anna'，'Anael'，'Analu'，'Andreas'，'Andrea'，'Andres'和'Anatole'，那么查找'And'会返回'Andreas' '，'Andrea'和'Andres'。
答案 1 :(得分：0)
有另一个按前缀索引的地图。特别是使用Guava的Multimap，它允许键映射到集合值。
答案 2 :(得分：0)
我写了自己的MapFilter。我主要用它来处理属性文件。基本上你选择一个共同的前缀 - 比如"com."并过滤你的地图，选择带有该前缀的所有条目。
此解决方案的优雅源于这样一个事实：过滤过程指向其底层地图的值，因此它确实是一个过滤器。此外，过滤过滤后的地图也具有效率优势。
/**
* Allows the filtering of maps by key prefix.
*
* Note that all access through the filter reference the underlying Map so
* adding to a MapFilder results in additions to the Map.
*
* @author OldCurmudgeon
* @param <T>
*/
public class MapFilter<T> implements Map<String, T> {
// The enclosed map -- could also be a MapFilter.
final private Map<String, T> map;
// Use a TreeMap for predictable iteration order.
// Store Map.Entry to reflect changes down into the underlying map.
// The Key is the shortened string. The entry.key is the full string.
final private Map<String, Map.Entry<String, T>> entries = new TreeMap<>();
// The prefix they are looking for in this map.
final private String prefix;
public MapFilter(Map<String, T> map, String prefix) {
// Store my backing map.
this.map = map;
// Record my prefix.
this.prefix = prefix;
// Build my entries.
rebuildEntries();
}
public MapFilter(Map<String, T> map) {
this(map, "");
}
private synchronized void rebuildEntries() {
// Start empty.
entries.clear();
// Build my entry set.
for (Map.Entry<String, T> e : map.entrySet()) {
String key = e.getKey();
// Retain each one that starts with the specified prefix.
if (key.startsWith(prefix)) {
// Key it on the remainder.
String k = key.substring(prefix.length());
// Entries k always contains the LAST occurrence if there are multiples.
entries.put(k, e);
}
}
}
@Override
public String toString() {
return "MapFilter(" + prefix + ") of " + map + " containing " + entrySet();
}
// Constructor from a properties file.
public MapFilter(Properties p, String prefix) {
// Properties extends HashTable<Object,Object> so it implements Map.
// I need Map<String,T> so I wrap it in a HashMap for simplicity.
// Java-8 breaks if we use diamond inference.
this(new HashMap<>((Map) p), prefix);
}
// Helper to fast filter the map.
public MapFilter<T> filter(String prefix) {
// Wrap me in a new filter.
return new MapFilter<>(this, prefix);
}
// Count my entries.
@Override
public int size() {
return entries.size();
}
// Are we empty.
@Override
public boolean isEmpty() {
return entries.isEmpty();
}
// Is this key in me?
@Override
public boolean containsKey(Object key) {
return entries.containsKey(key);
}
// Is this value in me.
@Override
public boolean containsValue(Object value) {
// Walk the values.
for (Map.Entry<String, T> e : entries.values()) {
if (value.equals(e.getValue())) {
// Its there!
return true;
}
}
return false;
}
// Get the referenced value - if present.
@Override
public T get(Object key) {
return get(key, null);
}
// Get the referenced value - if present.
public T get(Object key, T dflt) {
Map.Entry<String, T> e = entries.get((String) key);
return e != null ? e.getValue() : dflt;
}
// Add to the underlying map.
@Override
public T put(String key, T value) {
T old = null;
// Do I have an entry for it already?
Map.Entry<String, T> entry = entries.get(key);
// Was it already there?
if (entry != null) {
// Yes. Just update it.
old = entry.setValue(value);
} else {
// Add it to the map.
map.put(prefix + key, value);
// Rebuild.
rebuildEntries();
}
return old;
}
// Get rid of that one.
@Override
public T remove(Object key) {
// Do I have an entry for it?
Map.Entry<String, T> entry = entries.get((String) key);
if (entry != null) {
entries.remove(key);
// Change the underlying map.
return map.remove(prefix + key);
}
return null;
}
// Add all of them.
@Override
public void putAll(Map<? extends String, ? extends T> m) {
for (Map.Entry<? extends String, ? extends T> e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
// Clear everything out.
@Override
public void clear() {
// Just remove mine.
// This does not clear the underlying map - perhaps it should remove the filtered entries.
for (String key : entries.keySet()) {
map.remove(prefix + key);
}
entries.clear();
}
@Override
public Set<String> keySet() {
return entries.keySet();
}
@Override
public Collection<T> values() {
// Roll them all out into a new ArrayList.
List<T> values = new ArrayList<>();
for (Map.Entry<String, T> v : entries.values()) {
values.add(v.getValue());
}
return values;
}
@Override
public Set<Map.Entry<String, T>> entrySet() {
// Roll them all out into a new TreeSet.
Set<Map.Entry<String, T>> entrySet = new TreeSet<>();
for (Map.Entry<String, Map.Entry<String, T>> v : entries.entrySet()) {
entrySet.add(new Entry<>(v));
}
return entrySet;
}
/**
* An entry.
*
* @param <T>
*
* The type of the value.
*/
private static class Entry<T> implements Map.Entry<String, T>, Comparable<Entry<T>> {
// Note that entry in the entry is an entry in the underlying map.
private final Map.Entry<String, Map.Entry<String, T>> entry;
Entry(Map.Entry<String, Map.Entry<String, T>> entry) {
this.entry = entry;
}
@Override
public String getKey() {
return entry.getKey();
}
@Override
public T getValue() {
// Remember that the value is the entry in the underlying map.
return entry.getValue().getValue();
}
@Override
public T setValue(T newValue) {
// Remember that the value is the entry in the underlying map.
return entry.getValue().setValue(newValue);
}
@Override
public boolean equals(Object o) {
if (!(o instanceof Entry)) {
return false;
}
Entry e = (Entry) o;
return getKey().equals(e.getKey()) && getValue().equals(e.getValue());
}
@Override
public int hashCode() {
return getKey().hashCode() ^ getValue().hashCode();
}
@Override
public String toString() {
return getKey() + "=" + getValue();
}
@Override
public int compareTo(Entry<T> o) {
return getKey().compareTo(o.getKey());
}
}
// Simple tests.
public static void main(String[] args) {
String[] samples = {
"Some.For.Me",
"Some.For.You",
"Some.More",
"Yet.More"};
Map map = new HashMap();
for (String s : samples) {
map.put(s, s);
}
Map all = new MapFilter(map);
Map some = new MapFilter(map, "Some.");
Map someFor = new MapFilter(some, "For.");
System.out.println("All: " + all);
System.out.println("Some: " + some);
System.out.println("Some.For: " + someFor);
Properties props = new Properties();
props.setProperty("namespace.prop1", "value1");
props.setProperty("namespace.prop2", "value2");
props.setProperty("namespace.iDontKnowThisNameAtCompileTime", "anothervalue");
props.setProperty("someStuff.morestuff", "stuff");
Map<String, String> filtered = new MapFilter(props, "namespace.");
System.out.println("namespace props " + filtered);
}
}