Java for LeetCode 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.

解题思路：

参考百度百科：Trie树

已经给出了详细的代码：

JAVA实现如下：

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class TrieNode {     // Initialize your data structure here.     int num;// 有多少单词通过这个节点,即节点字符出现的次数     TrieNode[] son;// 所有的儿子节点     boolean isEnd;// 是不是最后一个节点     char val;// 节点的值       TrieNode() {         this.num = 1;         this.son = new TrieNode[26];         this.isEnd = false;     } }   public class Trie {     private TrieNode root;       public Trie() {         root = new TrieNode();     }       public void insert(String word) {         if (word == null || word.length() == 0)             return;         TrieNode node = this.root;         char[] letters = word.toCharArray();         for (int i = 0; i < word.length(); i++) {             int pos = letters[i] - 'a';             if (node.son[pos] == null) {                 node.son[pos] = new TrieNode();                 node.son[pos].val = letters[i];             } else {                 node.son[pos].num++;             }             node = node.son[pos];         }         node.isEnd = true;     }       // Returns if the word is in the trie.     public boolean search(String word) {         if (word == null || word.length() == 0) {             return false;         }         TrieNode node = root;         char[] letters = word.toCharArray();         for (int i = 0; i < word.length(); i++) {             int pos = letters[i] - 'a';             if (node.son[pos] != null) {                 node = node.son[pos];             } else {                 return false;             }         }         return node.isEnd;     }       // Returns if there is any word in the trie     // that starts with the given prefix.     public boolean startsWith(String prefix) {         if (prefix == null || prefix.length() == 0) {             return false;         }         TrieNode node = root;         char[] letters = prefix.toCharArray();         for (int i = 0; i < prefix.length(); i++) {             int pos = letters[i] - 'a';             if (node.son[pos] != null) {                 node = node.son[pos];             } else {                 return false;             }         }         return true;     } }   // Your Trie object will be instantiated and called as such: // Trie trie = new Trie(); // trie.insert("somestring"); // trie.search("key");