标签：node Node 数据结构 return Trie 恋上 value key null
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【恋上数据结构与算法】Trie
Trie
接口设计
public interface Trie<V> {
int size();
boolean isEmpty();
void clear();
V add(String key, V value); // 添加一个单词
V remove(String key); // 删除这个单词
V get(String key); // 拿到这个单词对应的value
boolean contains(String key); // 判断Trie中是否有这个单词
boolean startsWith(String prefix); // 判断Trie中是否有以这个单词为前缀的单词
}
实现
TrieMap_v0
public class TrieMap_v0<V> implements Trie<V> {
private int size;
private final Node<V> root = new Node<>();
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public void clear() {
root.getChildren().clear();
size = 0;
}
@Override
public V get(String key) {
final Node<V> node = node(key);
return node == null ? null : node.value;
}
@Override
public boolean contains(String key) {
return node(key) != null;
}
@Override
public boolean startsWith(String prefix) {
keyCheck(prefix);
Node<V> node = root;
for (int i = 0, len = prefix.length(); i < len; i++) {
char c = prefix.charAt(i);
Node<V> childNode = node.getChildren().get(c);
if (childNode == null) return false;
node = childNode;
}
return true;
}
@Override
public V add(String key, V value) {
keyCheck(key);
Node<V> node = root;
for (int i = 0, len = key.length(); i < len; i++) {
char c = key.charAt(i);
Node<V> childNode = node.getChildren().get(c);
if (childNode == null) {
childNode = new Node<>();
node.getChildren().put(c, childNode);
}
node = childNode;
}
if (node.isWord) {
V oldValue = node.value;
node.value = value;
return oldValue;
}
node.isWord = true;
node.value = value;
size++;
return null;
}
@Override
public V remove(String key) {
return null;
}
private Node<V> node(String key) {
keyCheck(key);
Node<V> node = root;
for (int i = 0, len = key.length(); i < len; i++) {
char c = key.charAt(i);
Node<V> childNode = node.getChildren().get(c);
if (childNode == null) return null;
node = childNode;
}
return node.isWord ? node : null;
}
private void keyCheck(String key) {
if (key == null || key.length() == 0) throw new IllegalArgumentException("Key must not be empty!");
}
private static class Node<V> {
HashMap<Character, Node<V>> children;
V value;
boolean isWord;
HashMap<Character, Node<V>> getChildren() {
if (null == children) children = new HashMap<>();
return children;
}
}
}
TrieMap
public class TrieMap<V> implements Trie<V> {
private int size;
private Node<V> root;
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public void clear() {
root = null;
size = 0;
}
@Override
public V get(String key) {
Node<V> node = node(key);
if (node != null && node.isWord) return node.value;
return null;
}
@Override
public boolean contains(String key) {
Node<V> node = node(key);
return node != null && node.isWord;
}
@Override
public boolean startsWith(String prefix) {
Node<V> node = node(prefix);
return node != null;
}
@Override
public V add(String key, V value) {
keyCheck(key);
if (null == root) root = new Node<>(null, null);
Node<V> node = root;
for (int i = 0, len = key.length(); i < len; i++) {
char c = key.charAt(i);
boolean childrenIsEmpty = (node.children == null);
Node<V> childNode = childrenIsEmpty ? null : node.children.get(c);
if (childNode == null) {
childNode = new Node<>(c, node);
(childrenIsEmpty ? node.children = new HashMap<>() : node.children).put(c, childNode);
}
node = childNode;
}
if (node.isWord) {
V oldValue = node.value;
node.value = value;
return oldValue;
}
node.isWord = true;
node.value = value;
size++;
return null;
}
@Override
public V remove(String key) {
Node<V> node = node(key);
if (null == node || !node.isWord) return null;
size--;
V oldValue = node.value;
if (null != node.children && !node.children.isEmpty()) { // 不是叶子节点
node.value = null;
node.isWord = false;
return oldValue;
}
// 是叶子节点，向上删除
Node<V> parent = node.parent;
while (parent != null) {
parent.children.remove(node.character);
if (!parent.children.isEmpty() || parent.isWord) break;
parent = parent.parent;
}
return oldValue;
}
private Node<V> node(String key) {
keyCheck(key);
Node<V> node = root;
for (int i = 0, len = key.length(); i < len; i++) {
if (node == null || node.children == null || node.children.isEmpty()) return null;
node = node.children.get(key.charAt(i));
}
return node;
}
private void keyCheck(String key) {
if (key == null || key.length() == 0) throw new IllegalArgumentException("Key must not be empty!");
}
private static class Node<V> {
HashMap<Character, Node<V>> children;
V value;
boolean isWord;
Node<V> parent;
Character character;
Node(Character character, Node<V> parent) {
this.character = character;
this.parent = parent;
}
}
}
总结
注意
- 解决问题时，将问题深思熟虑后进行分解，拆分为若干个子问题，然后逐个解决。
参考
小码哥李明杰老师课程: 恋上数据结构与算法 第一季.
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标签：node,Node,数据结构,return,Trie,恋上,value,key,null 来源： https://blog.csdn.net/weixin_44018671/article/details/121574197
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