/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.jena.atlas.lib;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* An implementation of a classic Trie, this is a mapping from strings to some
* value type optimized for fast prefix search and match. If you do not need
* prefix search then you should typically use a standard {@link Map} instead.
* <p>
* The empty or null string may be used as a special key to refer to the root
* node of the trie.
* </p>
* <p>
* A Trie cannot store null values since null is used as an internal marker to
* indicate that there is no value associated with a key. This is necessary
* because the nature of the data structure means that adding a key potentially
* adds multiple keys many of which will not be associated with a value.
* </p>
*
* @param <T>
* Type of the value stored.
*/
public final class Trie<T> {
private TrieNode<T> root = new TrieNode<>(null);
/**
* Adds a value to the trie overwriting any existing value
* <p>
* Note that a null value is treated as if the key does not actually exist
* in the tree so trying to add a null is a no-op. If you want to remove a
* key use the {@link #remove(String)} method instead.
* </p>
*
* @param key
* Key
* @param value
* Value
*/
public void add(String key, T value) {
if (value == null)
return;
TrieNode<T> n = this.moveToNode(key);
n.setValue(value);
}
/**
* Move to a node creating new nodes if necessary
*
* @param key
* Key
* @return Node
*/
private TrieNode<T> moveToNode(String key) {
TrieNode<T> current = this.root;
if (key == null)
return current;
for (int i = 0; i < key.length(); i++) {
current = current.moveToChild(key.charAt(i));
}
return current;
}
/**
* Try to find a node in the trie
*
* @param key
* Key
* @return Node or null if not found
*/
private TrieNode<T> find(String key) {
TrieNode<T> current = this.root;
if (key == null)
return current;
for (int i = 0; i < key.length(); i++) {
current = current.getChild(key.charAt(i));
if (current == null)
break;
}
return current;
}
/**
* Removes a value from the trie
* <p>
* This doesn't actually remove the key per-se rather sets the value
* associated with the key to null.
* </p>
*
* @param key
* Key
*/
public void remove(String key) {
TrieNode<T> n = this.find(key);
if (n != null) {
n.setValue(null);
}
}
/**
* Clear the Trie completely.
*/
public void clear() {
root = new TrieNode<>(null);
}
/**
* Clear the Trie completely.
*/
public boolean isEmpty() {
return ! root.hasValue() ;
}
/**
* Gets whether a key exists in the trie and has a non-null value mapped to
* it
*
* @param key
* Key
* @return True if the key exists and has a non-null value mapped to it
*/
public boolean contains(String key) {
return this.contains(key, true);
}
/**
* Gets whether a key exists in the trie and meets the given value criteria
*
* @param key
* Key
* @param requireValue
* If true a key must have a non-null value associated with it to
* be considered to be contained in the tree, if false then the
* key must merely map to a node in the trie
* @return True if the key exists and the value criteria is met, false
* otherwise
*/
public boolean contains(String key, boolean requireValue) {
TrieNode<T> n = this.find(key);
if (n == null)
return false;
if (requireValue) {
return n.hasValue();
} else {
return true;
}
}
/**
* Gets whether a key value pair are present in the trie
*
* @param key
* Key
* @param value
* Value
* @return True if the key value pair exists in the trie, false otherwise
*/
public boolean contains(String key, T value) {
TrieNode<T> n = this.find(key);
if (n == null)
return false;
if (value == null && !n.hasValue())
return true;
return value.equals(n.getValue());
}
/**
* Gets the value associated with a key
*
* @param key
* Key
* @return Value
*/
public T get(String key) {
TrieNode<T> n = this.find(key);
if (n == null)
return null;
return n.getValue();
}
/**
* Performs a prefix search and returns all values mapped under the given
* prefix. The entirety of the prefix must be matches, if you only want part
* of the prefix to be matched use the {@link #partialSearch(String)} method
* instead.
*
* @param prefix
* Prefix
* @return List of values associated with the given key
*/
public List<T> prefixSearch(String prefix) {
TrieNode<T> n = this.find(prefix);
if (n == null)
return new ArrayList<>();
return Collections.unmodifiableList(n.getValues());
}
/**
* Performs a search and returns any value associated with any partial or
* whole prefix of the key
*
* @param key
* Key
* @return List of values associated with any partial prefix of the key
*/
public List<T> partialSearch(String key) {
List<T> values = new ArrayList<>();
TrieNode<T> current = this.root;
if (key == null) {
if (current.hasValue())
values.add(current.getValue());
} else {
for (int i = 0; i < key.length(); i++) {
if (current.hasValue())
values.add(current.getValue());
current = current.getChild(key.charAt(i));
if (current == null)
return Collections.unmodifiableList(values);
}
// If we reach here current is the complete key match
// so make sure to include it in the values list
if (current.hasValue()) {
values.add(current.getValue());
}
}
return Collections.unmodifiableList(values);
}
/**
* Finds the shortest match for a given key i.e. returns the value
* associated with the shortest prefix of the key that has a value
*
* @param key
* Key
* @return Shortest Match or null if no possible matches
*/
public T shortestMatch(String key) {
TrieNode<T> current = this.root;
if (key == null)
return current.getValue();
for (int i = 0; i < key.length(); i++) {
if (current.hasValue())
break;
current = current.getChild(key.charAt(i));
if (current == null)
return null;
}
return current.getValue();
}
/**
* Finds the longest match for a given key i.e. returns the value associated
* with the longest prefix of the key that has a value
*
* @param key
* Key
* @return Longest Match or null if no possible matches
*/
public T longestMatch(String key) {
T value = null;
TrieNode<T> current = this.root;
if (key == null) {
return current.getValue();
} else {
for (int i = 0; i < key.length(); i++) {
if (current.hasValue())
value = current.getValue();
current = current.getChild(key.charAt(i));
if (current == null)
return value;
}
// If we reach here current is the complete key match
// so return its value if it has one
if (current.hasValue()) {
return current.getValue();
}
}
return value;
}
/**
* Represents a node in the Trie
* <p>
* The implementation is designed to be sparse such that we delay creation
* of things at both leafs and interior nodes until they are actually needed
* </p>
*
*/
private static class TrieNode<T> {
private Map<Character, TrieNode<T>> children = null;
private Character singletonChildChar = null;
private TrieNode<T> singletonChild = null;
private T value;
/**
* Creates a Trie Node
*
* @param value
* Value
*/
public TrieNode(T value) {
this.value = value;
}
/**
* Gets the value
*
* @return Value
*/
public T getValue() {
return this.value;
}
/**
* Sets the value
*
* @param value
* Value
*/
public void setValue(T value) {
this.value = value;
}
/**
* Returns whether a non-null value is associated with this node
*
* @return True if there is a non-null value, false otherwise
*/
public boolean hasValue() {
return this.value != null;
}
/**
* Gets the child (if it exists)
*
* @param c
* Character to move to
* @return Child
*/
public TrieNode<T> getChild(Character c) {
if (this.children != null) {
return this.children.get(c);
} else if (c.equals(this.singletonChildChar)) {
return this.singletonChild;
} else {
return null;
}
}
/**
* Moves to a child (creating a new node if necessary)
*
* @param c
* Character to move to
* @return Child
*/
public TrieNode<T> moveToChild(Character c) {
TrieNode<T> n = this.getChild(c);
if (n == null) {
n = new TrieNode<>(null);
if (this.children != null) {
// Add to existing map
this.children.put(c, n);
} else if (this.singletonChildChar != null) {
// Need to lazily create map
this.children = new HashMap<>();
this.children.put(this.singletonChildChar, this.singletonChild);
this.children.put(c, n);
} else {
// Singleton child
this.singletonChildChar = c;
this.singletonChild = n;
}
}
return n;
}
/**
* Gets all values from a given node and its descendants
*
* @return Values
*/
public List<T> getValues() {
List<T> values = new ArrayList<>();
if (this.hasValue()) {
values.add(this.value);
}
if (this.children != null) {
for (TrieNode<T> child : this.children.values()) {
values.addAll(child.getValues());
}
} else if (this.singletonChild != null) {
values.addAll(this.singletonChild.getValues());
}
return values;
}
}
}