208-implement-trie-prefix-tree.md

208. Implement Trie (Prefix Tree) - 实现 Trie (前缀树)

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

示例:

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。

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题目标签：Design / Trie

题目链接：LeetCode / LeetCode中国

题解

Language	Runtime	Memory
java	74 ms	52.2 MB

class Trie {
    
    class TrieNode {
        int path;
        int end;
        TrieNode map[];
        
        TrieNode() {
            path = 0;
            end = 0;
            map = new TrieNode[26];
        }
    }
    
    TrieNode root;

    /** Initialize your data structure here. */
    public Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        char[] w = word.toCharArray();
        TrieNode node = root;
        int index = 0;
        for (int i = 0; i< w.length; i++) {
            index = w[i] - 'a';
            if (node.map[index] == null) {
                node.map[index] = new TrieNode();
            }
            node = node.map[index];
            node.path++;
        }
        node.end++;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        char[] w = word.toCharArray();
        TrieNode node = root;
        int index = 0;
        for (int i = 0; i < w.length; i++) {
            index = w[i] - 'a';
            if (node.map[index] == null) {
                return false;
            }
            node = node.map[index];
        }
        return node.end > 0;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        char[] w = prefix.toCharArray();
        TrieNode node = root;
        int index = 0;
        for (int i = 0; i < w.length; i++) {
            index = w[i] - 'a';
            if (node.map[index] == null) {
                return false;
            }
            node = node.map[index];
        }
        return true;
    }
}

/**
 * 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);
 */