【62】208. Implement Trie (Prefix Tree)

208. Implement Trie (Prefix Tree)

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• Total Accepted: 63834
• Total Submissions: 245645
• Difficulty: Medium
• Contributors: Admin

 

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

Note:
You may assume that all inputs are consist of lowercase letters a-z.\

 

class TrieNode{
    public:
        bool isWord;
        TrieNode* child[26];
        TrieNode() : isWord(false){
            for(auto &a : child){//更改内容要用&
                a = NULL;
                
            }
        }  
};

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(char c : word){
            int i = c - 'a';
            if(p -> child[i] == NULL){
                p -> child[i] = new TrieNode();
            }
            p = p -> child[i];
        }
        p -> isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    bool search(string word) {
        TrieNode* p = root;
        for(char c : word){
            int i = c - 'a';
            if(!p -> child[i]) return false;
            p = p -> child[i];
        }
        //if(!p -> isWord) return false;
        //return true;
        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(char c : prefix){
            int i = c - 'a';
            if(!p -> child[i]) return false;
            p = p -> child[i];
        }
        //if(!p -> isWord) return false;
        return true;
        //return p -> isWord;
    }
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);
 */