Leetcode no. 208

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本文介绍了一个Trie树（前缀树）的实现方法，包括插入(insert)、搜索(search)及判断是否存在以某个字符串为前缀的单词(startsWith)等基本操作。

208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Note:
You may assume that all inputs are consist of lowercase letters a-z.

class TrieNode {
    // Initialize your data structure here.
    public char val;
    public TrieNode[] children= new TrieNode[26];
    public boolean isWord;
    public TrieNode(){}
    public TrieNode(char c) {
        this.val= c;
    }
}

public class Trie {
    private TrieNode root;

    public Trie() {
        root = new TrieNode();
        root.val= ' ';
    }

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

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

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

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");