208. Implement Trie (Prefix Tree)

原题链接：https://leetcode.com/problems/implement-trie-prefix-tree/description/
都是前缀树相关的题目。LeetCode 上面刷题时可以查看 Similar Questions 问题，这道题目也是做 211. Add and Search Word - Data structure design 这道题目看到的。
这道题目就很简单的，我之前已经专门看过了前缀树的实现了：http://www.cnblogs.com/optor/p/8513547.html
所以，这道题就是直接把之前的代码复制过来就好了：

class Trie {
    
    class TrieNode {

        // R links to node children
        private TrieNode[] links;

        private final int R = 26;

        private boolean isEnd;

        // number of children non null links
        private int size;

        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;
            size++;
        }

        public int getLinks() {
            return size;
        }

        public void setEnd() {
            isEnd = true;
        }

        public boolean isEnd() {
            return isEnd;
        }

    }
    
    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 (int i = 0; i < word.length(); i++) {
            char currentChar = word.charAt(i);
            if (!node.containsKey(currentChar)) {
                node.put(currentChar, new TrieNode());
            }
            node = node.get(currentChar);
        }
        node.setEnd();
    }
    
    private TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            char curLetter = word.charAt(i);
            if (node.containsKey(curLetter)) {
                node = node.get(curLetter);
            } else {
                return null;
            }
        }
        return node;
    }
    
    /** 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;
    }
}

/**
 * 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);
 */