字典树Trie(单词查找树)详解

struct TrieNode {
    TrieNode *sons[26];
    int flag = 0; // flag == 1表示有该单词（叶子节点）
    TrieNode() {
        memset(sons, 0, 26 * sizeof(TrieNode*));
    }
};

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 *cur = root;
        int len = (int) word.length();
        for (int i = 0; i < len; i++) {
            if (!cur->sons[word[i] - 'a']) cur->sons[word[i] - 'a'] = new TrieNode();
            cur = cur->sons[word[i] - 'a'];
        }
        cur->flag = 1;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode *cur = root;
        int len = (int) word.length();
        for (int i = 0; i < len; i++) {
            if (cur->sons[word[i] - 'a']) cur = cur->sons[word[i] - 'a'];
            else return false;
        }
        if (cur->flag) return true;
        else return false;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        TrieNode *cur = root;
        int len = (int) prefix.length();
        for (int i = 0; i < len; i++) {
            if (cur->sons[prefix[i] - 'a']) cur = cur->sons[prefix[i] - 'a'];
            else return false;
        }
        return true;
    }
};