Implement Trie (Prefix Tree) ——LeetCode

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

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

 

实现一个字典树。

好久不做题，没感觉啊，TreeNode用一个布尔变量表示是否是一个合法单词的结尾即可，一开始还用cnt来计数，search的时候比较麻烦。

class TrieNode {

    // Initialize your data structure here.

     TrieNode [] next;

    boolean valid;

    public TrieNode() {

        next = new TrieNode[26];

        valid=false;

    }

}



public class Trie {

    private TrieNode root;



    public Trie() {

        root = new TrieNode();

    }



    // Inserts a word into the trie.

    public void insert(String word) {

        TrieNode ptr = root;

        for(char c:word.toCharArray()){

            if(ptr.next[c-'a']==null){

                ptr.next[c-'a'] = new TrieNode();

            }

            ptr=ptr.next[c-'a'];

        }

        ptr.valid=true;

    }



    // Returns if the word is in the trie.

    public boolean search(String word) {

        int last = 0;

        TrieNode ptr = root;

        for(char c:word.toCharArray()){

            if(ptr==null||ptr.next[c-'a']==null){

                return false;

            }

            ptr=ptr.next[c-'a'];

        }

        return ptr.valid;

    }



    // Returns if there is any word in the trie

    // that starts with the given prefix.

    public boolean startsWith(String prefix) {

        TrieNode ptr = root;

        for(char c:prefix.toCharArray()){

            if(ptr==null||ptr.next[c-'a']==null){

                return false;

            }

            ptr=ptr.next[c-'a'];

        }

        return true;

    }

}



// Your Trie object will be instantiated and called as such:

// Trie trie = new Trie();

// trie.insert("somestring");

// trie.search("key");