Leetcode208: 实现Trie（前缀树）

class Trie {
public:
    /** Initialize your data structure here. */
    Trie() {
        root_ = new TrieNode();
    }

    /** Inserts a word into the trie. */
    void insert(string word) {
        TrieNode* p = root_;
        for (const char c : word) {
            if (!p->children[c - 'a']) {
                p->children[c - 'a'] = new TrieNode();
            }
            p = p->children[c - 'a'];
        }
        p->is_word = true;
    }

    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode* p = find(word);
        return (p && p->is_word);
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        return find(prefix) != nullptr;
    }

private:
    // two basic: is_word: whether it is the end of a word
    // children : implement it with vector, storing the pointer to the child nodes
    struct TrieNode {
        bool is_word;
        vector<TrieNode*> children;
        TrieNode():is_word(false),children(26,nullptr){}

        ~TrieNode() {
            for (auto child : children) {
                if (child) delete child;
            }
        }
    };

    // common function for realizing search & startwith
    TrieNode* find(const string& prefix) {
        TrieNode* p = root_;
        for (char c : prefix) {
            p = p->children[c - 'a'];
            if (p == nullptr) break;
        }
        return p;
    }

    TrieNode* root_;
};

【思路】
前缀树的基本结构是一个最多有26个children的树