Implement Trie (Prefix Tree)

Trie 树实现

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

class TrieNode {
public:
    // Initialize your data structure here.

    TrieNode *child[26];
    bool isWord;
    TrieNode():isWord(false){
        for(auto &a : child)
            a = nullptr;
    }
};

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

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode* p = root;
        for(auto &a : word){
            int i = a - 'a';
            if(!p->child[i]) p->child[i] = new TrieNode();
            p = p->child[i];
        }
        p->isWord = true;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode* p = root;
        for(auto &a : word){
            int i = a - 'a';
            if(!p->child[i]) return false;
            p = p->child[i];
        }
        return p->isWord;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        TrieNode* p = root;
        for(auto &a : prefix){
            int i = a - 'a';
            if(!p->child[i]) return false;
            p = p->child[i];
        }
        return true;
    }

private:
    TrieNode* root;
};

参看：http://www.cnblogs.com/grandyang/p/4491665.html