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;
    }
}