208. Implement Trie (Prefix Tree)

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

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

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Trie的基本实现：

struct TrieNode{
    TrieNode* children[26];
    bool isWord;
    TrieNode(){
        for(int i=0;i<26;i++){
            children[i]=NULL;
        }
    }
    ~TrieNode(){
        for(int i=0;i<26;i++){
            delete children[i];
        }
    }
};
class Trie {
private:
    TrieNode* root;
public:
    /** Initialize your data structure here. */
    Trie() {
        root = new TrieNode();
    }
    
    /** Inserts a word into the trie. */
    void insert(string word) {
        TrieNode* curr = root;
        for(auto c: word){
            if(curr->children[c-'a']==NULL){
                curr->children[c-'a'] = new TrieNode();
            }
            curr = curr->children[c-'a'];
        }
        curr->isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode* curr = root;
        for(auto c: word){
            if(curr->children[c-'a']==NULL){
                return false;  
            }
            curr = curr->children[c-'a'];
        }
        
        return curr->isWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        TrieNode* curr = root;
        for(auto c: prefix){
            if(curr->children[c-'a']==NULL){
                return false;
            }
            curr=curr->children[c-'a'];
        }
        
        return true;
    }
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * bool param_2 = obj.search(word);
 * bool param_3 = obj.startsWith(prefix);
 */