[LeetCode] 208. Implement Trie (Prefix Tree)

思路:
参考https://discuss.leetcode.com/topic/13463/maybe-the-code-is-not-too-much-by-using-next-26-c/14. 很简单直接. 关键是要想到每个树节点的结构, 每个节点要有一个长度为26的数组, 然后再加一个布尔值记录到达这里是否是单词.

class TrieNode {
public:
    // Initialize your data structure here.
    TrieNode() {
        memset(children, NULL, sizeof(children));
        isWord = false;
    }

    TrieNode* children[26];
    bool isWord;
};

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

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode* node = root;
        for (int i = 0; i < word.length(); i++) {
            if (! node->children[word[i] - 'a'])
                node->children[word[i] - 'a'] = new TrieNode();
            node = node->children[word[i] - 'a'];
        }
        node->isWord = true;
    }

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

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

private:
    TrieNode* find(string s) {
        TrieNode* node = root;
        for (int i = 0; i < s.length(); i++) {
            if (node->children[s[i] - 'a'])
                node = node->children[s[i] - 'a'];
            else
                return NULL;
        }
        return node;
    }

private:
    TrieNode* root;
};