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0208_implement_trie.java
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129 lines (108 loc) · 3.27 KB
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/*
实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。
示例:
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple"); // 返回 true
trie.search("app"); // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");
说明:
1. 你可以假设所有的输入都是由小写字母 a-z 构成的。
2. 保证所有输入均为非空字符串。
*/
class MyTrie {
class TrieNode {
public Map<Character, TrieNode> children;
public boolean isEnd = false;
public TrieNode() {
children = new HashMap<>();
}
}
private TrieNode root;
/** Initialize your data structure here. */
public Trie() {
root = new TrieNode();
}
/** Inserts a word into the trie. */
public void insert(String word) {
TrieNode node = root;
for (int i = 0; i < word.length(); i++) {
char c = word.charAt(i);
if (!node.children.containsKey(c))
node.children.put(c, new TrieNode());
node = node.children.get(c);
}
node.isEnd = true;
}
/** Returns if the word is in the trie. */
public boolean search(String word) {
TrieNode node = root;
for (int i = 0; i < word.length(); i++) {
if (!node.children.containsKey(word.charAt(i)))
return false;
node = node.children.get(word.charAt(i));
}
return node.isEnd == true;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
TrieNode node = root;
for (int i = 0; i < prefix.length(); i++) {
if (!node.children.containsKey(prefix.charAt(i)))
return false;
node = node.children.get(prefix.charAt(i));
}
return true;
}
}
class Trie1 {
/** Initialize your data structure here. */
class Node{
Node[] nodes;
boolean isEnd;
public Node(){
nodes=new Node[26];
}
}
private Node root;
public Trie() {
root=new Node();
}
/** Inserts a word into the trie. */
public void insert(String word) {
Node t=root;
for(int i=0;i<word.length();i++){
int index=word.charAt(i)-'a';
if(t.nodes[index]==null){
t.nodes[index]=new Node();
}
t=t.nodes[index];
}
t.isEnd=true;
}
/** Returns if the word is in the trie. */
public boolean search(String word) {
Node t=root;
for(int i=0;i<word.length();i++){
int index=word.charAt(i)-'a';
if(t.nodes[index]==null){
return false;
}
t=t.nodes[index];
}
return t.isEnd==true;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String word) {
Node t=root;
for(int i=0;i<word.length();i++){
int index=word.charAt(i)-'a';
if(t.nodes[index]==null){
return false;
}
t=t.nodes[index];
}
return true;
}
}