春招修仙系列 —— leetcode 208实现 Trie（前缀树）

题目：

实现一个 Trie (前缀树)，包含 insert, search, 和 startsWith 这三个操作。

示例 1:

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。

代码1：

class Trie {
  private TrieNode root;

  /** Initialize your data structure here. */
  public Trie() {
    root = new TrieNode();
    root.val = ' ';
  }

  /** Inserts a word into the trie. */
  public void insert(String word) {
    TrieNode ws = root;
    for (int i = 0; i < word.length(); i++) {
      char c = word.charAt(i);
      if (ws.children[c - 'a'] == null) {
        ws.children[c - 'a'] = new TrieNode(c);
      }
      ws = ws.children[c - 'a'];
    }
    ws.isWord = true;
  }

  /** Returns if the word is in the trie. */
  public boolean search(String word) {
    TrieNode ws = root;
    for (int i = 0; i < word.length(); i++) {
      char c = word.charAt(i);
      if (ws.children[c - 'a'] == null) return false;
      ws = ws.children[c - 'a'];
    }
    return ws.isWord;
  }

  /** Returns if there is any word in the trie that starts with the given prefix. */
  public boolean startsWith(String prefix) {
    TrieNode ws = root;
    for (int i = 0; i < prefix.length(); i++) {
      char c = prefix.charAt(i);
      if (ws.children[c - 'a'] == null) return false;
      ws = ws.children[c - 'a'];
    }
    return true;
  }
}

class TrieNode {
  public char val;
  public boolean isWord;
  public TrieNode[] children = new TrieNode[26];

  public TrieNode() {}

  public TrieNode(char c) {
    TrieNode node = new TrieNode();
    node.val = c;
  }
}

/**
 * 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);
 */

结果：