LeetCode Implement Trie (Prefix Tree) （实现trie树3个函数：插入，查找，前缀）

题意：实现trie树的3个功能，只含小写字母的串。

思路：老实做即可！

class TrieNode {
public:
    TrieNode*  chd[26];
    bool flag;
    // Initialize your data structure here.
    TrieNode() {
        memset(chd,0,sizeof(chd));
        flag=0;
    }

};

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

    // Inserts a word into the trie.
    void insert(string word) {
        int p=0;
        TrieNode* tmp=root;
        while(p<word.size())
        {
            if(!tmp->chd[word[p]-'a'])
            {
                TrieNode* newnode=new TrieNode();
                tmp->chd[word[p]-'a']=newnode;
            }
            tmp=tmp->chd[word[p]-'a'];
            p++;
        }
        tmp->flag=1;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        int p=0;
        TrieNode* tmp=root;
        while(p<word.size())
        {
            //cout<<word[p]<<" ";
            if(tmp->chd[word[p]-'a'])    tmp=tmp->chd[word[p]-'a'];
            else return false;
            p++;
        }
        if(tmp->flag==1) return true;
        return false;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        int p=0;
        TrieNode* tmp=root;
        while(p<prefix.size())
        {
            if(tmp->chd[prefix[p]-'a'])    tmp=tmp->chd[prefix[p]-'a'];
            else return false;
            p++;
        }
        return true;
    }

private:
    TrieNode* root;
};