208.Implement Trie (Prefix Tree)

Tags: Trie Medium

Links: https://leetcode.com/problems/implement-trie-prefix-tree/

---

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

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

• You may assume that all inputs are consist of lowercase letters a-z.
• All inputs are guaranteed to be non-empty strings.

---

class TrieNode{
public:
    TrieNode *child[26];
    bool isWord; //到当前字符为止是否是一个完整的单词

    TrieNode() : isWord(false) {
        for (auto & a : child) a = nullptr;
    }
};

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 (auto &a : word){
            int id = a - 'a';
            if (!p -> child[id]) p -> child[id] = new TrieNode();
            p = p -> child[id];
        }

        p -> isWord = true;
    }

    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode *p = root;

        for (auto a : word){
            int id = a - 'a';
            if (!p -> child[id]) return false;
            p = p -> child[id];
        }

        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 id = a - 'a';
            if (!p -> child[id]) return false;
            p = p -> child[id];
        }

        return true;
    }

private:
    TrieNode *root;
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */