Implement Trie（LintCode）

Implement Trie

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

样例

 

注意

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

百度了一下，了解了字典树是啥，然后看了下实现的代码，然后自己写还是不难的（是啊，知道答案当然不会觉得难）。

字典树

又称单词查找树，Trie树，是一种树形结构，是一种哈希树的变种。典型应用是用于统计，排序和保存大量的字符串（但不仅限于字符串），所以经常被搜索引擎系统用于文本词频统计。它的优点是：利用字符串的公共前缀来减少查询时间，最大限度地减少无谓的字符串比较，查询效率比哈希树高。

 

详细的可以看百度百科

 /**
  * Your Trie object will be instantiated and called as such:
  * Trie trie = new Trie();
  * trie.insert("lintcode");
  * trie.search("lint"); will return false
  * trie.startsWith("lint"); will return true
  */
 class TrieNode {
     // Initialize your data structure here.
     char val;
     boolean isEnd;
     int SIZE = 26;
     TrieNode[] children;

     public TrieNode() {
         children = new TrieNode[SIZE];
         isEnd = false;
     }
     public TrieNode(char val) {
         children = new TrieNode[SIZE];
         this.val = val;
         isEnd = false;
     }
 }

 public class Solution {
     private TrieNode root;

     public Solution() {
         root = new TrieNode();
     }

     // Inserts a word into the trie.
     public void insert(String word) {
         if(word == null || word.length() == 0) return;
         char[] cs = word.toCharArray();
         TrieNode p = root;
         for(int i=0;i<cs.length;i++) {
             int pos = cs[i] - 'a';
             if(p.children[pos] == null) {
                 p.children[pos] = new TrieNode(cs[i]);
             }
             p = p.children[pos];
         }
         if(!p.isEnd) p.isEnd = true;
     }

     // Returns if the word is in the trie.
     public boolean search(String word) {
         if(word == null || word.length() == 0) return false;
         char[] cs = word.toCharArray();
         TrieNode p = root;
         for(int i=0;i<cs.length;i++){
             int pos = cs[i] - 'a';
             if(p.children[pos] != null) {
                 p = p.children[pos];
             }else return false;
         }
         return p.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;
         char[] cs = prefix.toCharArray();
         TrieNode p = root;
         for(int i=0;i<cs.length;i++){
             int pos = cs[i] - 'a';
             if( p.children[pos] != null) {
                 p = p.children[pos];
             }else return false;
         }
         return true;
     }
 }