leetcode.208. Implement Trie (Prefix Tree) 字典树

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

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

class TrieNode {
public:
    // Initialize your data structure here.
     bool isEnd;  
    TrieNode *children[26];  
    TrieNode() : isEnd(false)  
    {  
        for (int i = 0; i < 26; i++)  
        {  
            children[i] = NULL;  
        }  
    }  
};

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

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode *cur = root;  
        for (int i = 0; i < word.length(); i++)  
        {  
            int index = word[i] - 'a';  
            if (cur->children[index] == NULL)  
            {  
                cur->children[index] = new TrieNode();  
            }  
  
            cur = cur->children[index];  
        }  
  
        cur->isEnd = true;   
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        int n = word.length();  
        return search(word, n, 0, root); 
        
    }
     bool search(string &word, int n, int pos, TrieNode *cur)  
    {  
        if (cur == NULL)  return false;  
          
        if (pos == n)   return cur->isEnd;  
          
        int index = word[pos] - 'a';  
        if (cur->children[index])  
        {  
            return search(word, n, pos+1, cur->children[index]);  
        }  

        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(int i = 0;i<prefix.size();i++)
         {
             int index = prefix[i] - 'a';  
             if (cur->children[index] == NULL)  
                return false; 
              cur = cur->children[index]; 
         }
         
         return true;
    }

private:
    TrieNode* root;
};

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