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_208_Trie.java
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_208_Trie.java
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package pp.arithmetic.leetcode;
import pp.arithmetic.model.TrieTree;
/**
* Created by wangpeng on 2018/9/28.
* 208.实现 Trie (前缀树)
* <p>
* 实现一个 Trie (前缀树),包含 insert, search, 和 startsWith 这三个操作。
* <p>
* 示例:
* <p>
* Trie trie = new Trie();
* <p>
* 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:
* <p>
* 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。
*
* @see <a href="https://leetcode-cn.com/problems/implement-trie-prefix-tree/description/">implement-trie-prefix-tree</a>
*/
public class _208_Trie {
public static void main(String[] args) {
Trie trie = new Trie();
trie.insert("apple");
System.out.println(trie.search("apple")); // 返回 true
System.out.println(trie.search("app")); // 返回 false
System.out.println(trie.startsWith("app")); // 返回 true
trie.insert("app");
System.out.println(trie.search("app")); //true
}
public static class Trie {
private TrieTree root;
/**
* Initialize your data structure here.
*/
public Trie() {
root = new TrieTree('0');
}
/**
* Inserts a word into the trie.
*/
public void insert(String word) {
char[] chars = word.toCharArray();
TrieTree node = root;
for (int i = 0; i < chars.length; i++) {
TrieTree[] tries = node.tries;
int index = chars[i] - 'a';
if (tries[index] == null) {
tries[index] = new TrieTree(chars[i]);
}
node = tries[index];
}
node.isEnd = true;
}
/**
* Returns if the word is in the trie.
*/
public boolean search(String word) {
char[] chars = word.toCharArray();
TrieTree node = root;
for (int i = 0; i < chars.length; i++) {
TrieTree[] tries = node.tries;
int index = chars[i] - 'a';
TrieTree temp = tries[index];
if (temp == null) {
return false;
}
node = temp;
}
return node.isEnd;
}
/**
* Returns if there is any word in the trie that starts with the given prefix.
*/
public boolean startsWith(String prefix) {
char[] chars = prefix.toCharArray();
TrieTree node = root;
for (int i = 0; i < chars.length; i++) {
TrieTree[] tries = node.tries;
int index = chars[i] - 'a';
TrieTree temp = tries[index];
if (temp == null) {
return false;
}
node = temp;
}
return true;
}
}
}