208. 实现 Trie (前缀树)
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");
trie.search("app"); // 返回 true
说明:
你可以假设所有的输入都是由小写字母 a-z 构成的。
保证所有输入均为非空字符串。
class Trie {
class Node {
boolean isWord;
Node[] next = new Node[26];
}
Node root = new Node();
/** Initialize your data structure here. */
public Trie() {
}
/** Inserts a word into the trie. */
public void insert(String word) {
Node p = root;
for(char ch : word.toCharArray()) {
if(p.next[ch - 'a'] == null)
p.next[ch - 'a'] = new Node();
p = p.next[ch - 'a'];
}
p.isWord = true;
}
/** Returns if the word is in the trie. */
public boolean search(String word) {
Node p = root;
for(char ch : word.toCharArray()) {
if(p.next[ch - 'a'] == null)
return false;
p = p.next[ch - 'a'];
}
return p.isWord;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
Node p = root;
for(char ch : prefix.toCharArray()) {
if(p.next[ch - 'a'] == null)
return false;
p = p.next[ch - 'a'];
}
return true;
}
}
/**
* Your Trie object will be instantiated and called as such:
* Trie obj = new Trie();
* obj.insert(word);
* boolean param_2 = obj.search(word);
* boolean param_3 = obj.startsWith(prefix);
*/
