208. Implement Trie (Prefix Tree)

problem

solution

先定義TrieNode 資料結構
Trie 只有葉子才會存資料，其餘只是指標

struct TrieNode{
    TrieNode* child[26];
    bool isWord;
    TrieNode():isWord(false){
        for(TrieNode* &c:child) c= nullptr;
    }
    
};
class Trie {
private:
    TrieNode * root;
public:
    Trie() {
        root = new TrieNode();
    }
    
    void insert(string word) {
        TrieNode *cur = root;
        for(char c:word){
            if(!cur->child[c-'a']) cur->child[c-'a'] = new TrieNode();
            cur = cur->child[c-'a'];
        }
        cur->isWord = true;
    }
    
    bool search(string word) {
        TrieNode *cur = root;
        for(char c:word){
            if(!cur->child[c-'a']) return false;
            cur = cur->child[c-'a'];
        }
        return cur->isWord;
    }
    
    bool startsWith(string prefix) {
        TrieNode *cur = root;
        for(char c:prefix){
            if(!cur->child[c-'a']) return false;
            cur = cur->child[c-'a'];
        }
        return true;
    }
};

analysis

search、insert、startWith operation

• time complexity O(n) , n = len(word)