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

208. 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);
 */