Leetcode/各大家 -- 208. Implement Trie (Prefix Tree)

208. Implement Trie (Prefix Tree)

• Difficulty: Medium

https://leetcode.com/problems/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.

 

Company Uber Facebook Twitter Microsoft Bloomberg 

Editorial Solution: https://leetcode.com/articles/implement-trie-prefix-tree/ 

分析： Trie is a tree data structure, which is used for retrieval of a key in a dataset of strings.应用在 Autocomplete，spell-check等 

Efficient in: * Finding all keys with a common prefix. *lexicographical order(字典顺序 aab < ab < b.)

思路: Each Tire node can have maximum R(26 for alphabet) links.

-- Insert string by char into tree, if null, create new TrieNode .Once reach end char mark the isEnd true

-- Search the last char must have the isEnd for true

Complexity: O(M=key_length) for insertion & search, M is the length of key

                    Space: O(alphabet(26)*M*N) N is number of keys in trie

关键字：Trie 

相关题： Trie with back-tracking F家
http://rainykat.blogspot.com/2017/01/leetcodef-211-add-and-search-word-data.html

public class Trie {
    class TrieNode {
        // Initialize your data structure here.
        //R links to node children
        private TrieNode[] links = new TrieNode[26];//simplified to save code
        private boolean isEnd;
    }
    private TrieNode 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 cur = word.charAt(i);
            if(node.links[cur-'a']==null) //char to index 
                node.links[cur-'a']= new TrieNode();//default constructor make copy of instance vars
            node = node.links[cur-'a'];
        }
        node.isEnd = true;
    }

    // Returns if the word is in the trie.
    public boolean search(String word) {
        TrieNode node = root;
        for(int i=0;i<word.length();i++){
            char cur = word.charAt(i);
            if(node.links[cur-'a']==null)return false;
            node = node.links[cur-'a'];
        }
        return node.isEnd;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    public boolean startsWith(String prefix) {
        TrieNode node = root;
        for(int i=0;i<prefix.length();i++){
            char cur = prefix.charAt(i);
            if(node.links[cur-'a']==null)return false;
            node = node.links[cur-'a'];
        }
        return true;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");