Implement Trie

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

http://www.lintcode.com/en/problem/implement-trie/

Solution

/**
 * Your Trie object will be instantiated and called as such:
 * Trie trie;
 * trie.insert("lintcode");
 * trie.search("lint"); will return false
 * trie.startsWith("lint"); will return true
 */
class TrieNode {
public:
    // Initialize your data structure here.
    TrieNode() {
        is_word = false;
    }
    bool is_word;
    unordered_map<char, TrieNode*> neighbors;
};

class Trie {
public:
    Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode *cur = root;
        for(auto const& c : word) {
            if(cur->neighbors.find(c) == cur->neighbors.end()) {
                TrieNode *newnode = new TrieNode();
                cur->neighbors[c] = newnode;
            } 
            cur = cur->neighbors[c];
        }
        cur->is_word = true;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode *cur = root;
        //return searchDFS(word, 0, cur);
        for(auto const& c : word) {
            if(cur->neighbors.find(c) == cur->neighbors.end()) {
                return false;
            }
            cur = cur->neighbors[c];
        }
        return cur->is_word;
        //return false;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        TrieNode *cur = root;
        for(auto const& c : prefix) {
            if(cur->neighbors.find(c) == cur->neighbors.end()) {
                return false;
            }
            cur = cur->neighbors[c];
        }
        return true;
    }

private:
    TrieNode* root;
    //也可以用递归实现search
    bool searchDFS(string& word, int pos, TrieNode* cur) {
        if(pos == word.length()) {
            return cur->is_word;
        }
        if(cur->neighbors.find(word[pos]) == cur->neighbors.end())
            return false;
        return searchDFS(word, pos+1, cur->neighbors[word[pos]]);
    }
};