# 算法 leetcode208 实现前缀树

``````public class Trie {
class TrieNode {
Map<Character, TrieNode> next = new HashMap<>();
boolean isEnd = false;
public TrieNode() {
}

}

private final TrieNode root = new TrieNode();
/** Inserts a word into the trie. */
public void insert(String word) {
if (word == null || word.isEmpty()) {
return;
}
TrieNode node = root;
char[] chs = word.toCharArray();
for (int i = 0; i < word.length(); i++) {
if (node != null && !node.next.containsKey(chs[i])) {
TrieNode trieNode = new TrieNode();
node.next.put(chs[i], trieNode);
node = trieNode;
} else {
node = node.next.get(chs[i]);
}
}
node.isEnd = true;
}

/** Returns if the word is in the trie. */
public boolean search(String word) {
if (word == null || word.isEmpty()) {
return false;
}
TrieNode node = root;
char[] chs = word.toCharArray();
for (int i = 0; i < word.length(); i++) {
if (node != null && !node.next.containsKey(chs[i])) {
return false;
} else {
node = node.next.get(chs[i]);
}
}
return node.isEnd;
}

/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
if (prefix == null || prefix.isEmpty()) {
return false;
}
TrieNode node = root;
char[] chs = prefix.toCharArray();
for (int i = 0; i < prefix.length(); i++) {
if (node != null && !node.next.containsKey(chs[i])) {
return false;
} else {
node = node.next.get(chs[i]);
}
}
return true;
}

public static void main(String[] args) {
Trie testTire = new Trie();
testTire.insert("word");
testTire.insert("phone");
testTire.insert("computer");
boolean search = testTire.search("word");
boolean startsWith = testTire.startsWith("ph");
}
}
``````

``````class Trie {
private Trie[] children;
private boolean isEnd;

public Trie(){
children = new Trie[26];
isEnd = false;
}

public void insert(String word) {
Trie node = this;
for (int i = 0; i < word.length(); i++) {
char ch = word.charAt(i);
int index = ch - 'a';
if (node.children[index] == null) {
node.children[index] = new Trie();
}
node = node.children[index];
}
node.isEnd = true;
}

boolean search(String word){
Trie node = searchPrefix(word);
return node != null && node.isEnd;
}

boolean startsWith(String prefix){
Trie node = searchPrefix(prefix);
return node != null;
}

Trie searchPrefix(String prefix) {
Trie node = this;
for (int i = 0; i < prefix.length(); i++) {
char ch= prefix.charAt(i);
int index = ch - 'a';
if(node.children[index] == null){
return null;
}
node = node.children[index];
}
return node;
}
}
``````