【刷题-LeetCode】208. Implement Trie (Prefix Tree)

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.

解

class trie_node{

public:

    vector<trie_node*>child; // 根据当前字符选取下一个节点，如果当前字符是a，接下来就往child['a']的分支走

    bool isWord; // 表明到达该节点时，是否包含了一个完整的单词

    // 构造函数

    trie_node(): isWord(false), child(26, NULL){}

    // 析构函数

    ~trie_node(){

        for(auto &c : child)delete c;

    }

};

class Trie {

public:

    trie_node* root;

    /** Initialize your data structure here. */

    // 构造函数

    Trie() {

        root = new trie_node();

    }

    /** Inserts a word into the trie. */

    void insert(string word) {

        trie_node *cur = root;

        for(int i = 0; i < word.size(); ++i){

            int idx = word[i] - 'a';

            if(cur->child[idx] == NULL){

                cur->child[idx] = new trie_node();

            }

            cur = cur->child[idx];

        }

        cur->isWord = true;

    }

    /** Returns if the word is in the trie. */

    bool search(string word) {

        trie_node *cur = root;

        for(auto ch : word){

            int idx = ch - 'a';

            if(cur->child[idx] == NULL)return false;

            cur = cur->child[idx];

        }

        return cur->isWord;

    }

    /** Returns if there is any word in the trie that starts with the given prefix. */

    bool startsWith(string prefix) {

        trie_node *cur = root;

        for(auto ch : prefix){

            int idx = ch - 'a';

            if(cur->child[idx] == NULL)return false;

            cur = cur->child[idx];

        }

        return true;

    }

};

/**

 * 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);

 */

巴特西

【刷题-LeetCode】208. Implement Trie (Prefix Tree)

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