208. Implement Trie (Prefix Tree)

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#Implement Trie Prefi

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本文介绍了一种使用Trie树的数据结构实现，包括插入(insert)、查找(search)和前缀匹配(startsWith)等基本操作。该实现假设所有输入由小写字母a-z组成。

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

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

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Solution:

Tips:

Trie tree

Java Code:

public class Trie {
    private TrieNode[] head;
    /** Initialize your data structure here. */
    public Trie() {
        head = new TrieNode[256];
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        TrieNode[] tail = head;
        TrieNode node = null;
        for (int i = 0; i < word.length(); i++) {
            char c = word.charAt(i);
            node = tail[c];
            if (node == null) {
                node = new TrieNode(c);
                tail[c] = node;
            }
            tail = node.next;
        }
        node.endFlg = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        TrieNode[] p = head;
        int i = 0;
        TrieNode node = null;
        for (; i < word.length(); i++) {
            char c = word.charAt(i);
            node = p[c];
            if (null == node || node.c != c) {
                break;
            } 
            
            p = p[c].next;
        }
        
        return i == word.length() && node.endFlg;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        TrieNode[] p = head;
        int i = 0;
        for (; i < prefix.length(); i++) {
            char c = prefix.charAt(i);
            if (p[c] == null || p[c].c != c) {
                break;
            } 
            
            p = p[c].next;
        }
        
        return i == prefix.length();
    }
    
    public static class TrieNode {
        public TrieNode(char c) {
            this.c = c;
        }
        public char c;
        public boolean endFlg = false;
        public TrieNode[] next = new TrieNode[256];
    }
}

/**
 * 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);
 */