题目描述
Trie（发音类似 "try"）或者说 前缀树 是一种树形数据结构，用于高效地存储和检索字符串数据集中的键。这一数据结构有相当多的应用情景，例如自动补完和拼写检查。
请你实现 Trie 类：
Trie() 初始化前缀树对象。void insert(String word) 向前缀树中插入字符串 word 。boolean search(String word) 如果字符串 word 在前缀树中，返回 true（即，在检索之前已经插入）；否则，返回 false 。boolean startsWith(String prefix) 如果之前已经插入的字符串 word 的前缀之一为 prefix ，返回 true ；否则，返回 false 。
示例：
输入
["Trie", "insert", "search", "search", "startsWith", "insert", "search"][[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
输出
[null, null, true, false, true, null, true]
解释
Trie trie = new Trie();trie.insert("apple");trie.search("apple"); // 返回 Truetrie.search("app"); // 返回 Falsetrie.startsWith("app"); // 返回 Truetrie.insert("app");trie.search("app"); // 返回 True
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代码
class Trie { 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 (char ch : word.toCharArray()) { if (!node.containsKey(ch)) { node.put(ch, new TrieNode()); } node = node.get(ch); } node.setEnd(); } /** Returns if the word is in the trie. */ public boolean search(String word) { TrieNode node = searchPrefix(word); return node != null && node.isEnd(); } /** Returns if there is any word in the trie that starts with the given prefix. */ public boolean startsWith(String prefix) { TrieNode node = searchPrefix(prefix); return node != null; }
public TrieNode searchPrefix(String prefix) { TrieNode node = root; for (char c : prefix.toCharArray()) { if (node.containsKey(c)) { node = node.get(c); } else { return null; } } return node; }}
class TrieNode { private TrieNode[] links; private final int R = 26; private boolean isEnd; public TrieNode () { links = new TrieNode[R]; }
public boolean containsKey(char ch) { return links[ch - 'a'] != null; }
public TrieNode get(char ch) { return links[ch - 'a']; }
public void put(char ch, TrieNode node) { links[ch - 'a'] = node; }
public void setEnd() { isEnd = true; }
public boolean isEnd() { return isEnd; }}
/** * 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); */
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总结
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