字典树

#define MAX_SIZE 26
class TrieNode {
public:
    TrieNode *child[MAX_SIZE];
    bool isWord;
    TrieNode() : isWord(false){
        for (int i=0;i<MAX_SIZE;i++)
            child[i]=NULL;
    }
};

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


    void insert(string s) {
        TrieNode *p = root;
        for (int i=0;i<s.length();i++) {
            int id = s[i] - 'a';
            if (!p->child[id]) 
                p->child[id] = new TrieNode();
            p = p->child[id];
        }
        p->isWord = true;
    }


    bool search(string key) {
        TrieNode *p = root;
        for (int i=0;i<key.length();i++) {
            int id = key[i] - 'a';
            if (!p->child[id]) 
                return false;
            p = p->child[id];
        }
        return p->isWord;
    }

    //和search()几乎一样，只是最后返回值不一样
    bool startsWith(string prefix) {
        TrieNode *p = root;
        for (int i=0;i<prefix.length();i++) {
            int id = prefix[i] - 'a';
            if (!p->child[id]) 
                return false;
            p = p->child[id];
        }
        return true;
    }

private:
    TrieNode* root;
};