208. implement trie (prefix tree) - attach detailed notes

class Trie {
    
private:
    vector<Trie*> vecTree;  // Prefix number of child nodes , Generally speaking, there are 26 individual 
    bool isEnd; // If the point is the last node of a string , Then the value is true, Otherwise false
    Trie* searchPrefix(string prefix){
      // because search and startsWith There is commonality , Sum it up into a function 
        Trie* node = this;
        for(char c : prefix){
    
        //  Compare with the prefix tree layer by layer in the string 
            c = c - 'a';
            if(node -> vecTree[c] == nullptr){
    
            //  If it doesn't exist , That is, the prefix does not exist , Returns an empty 
                return nullptr;
            }
            //  Enter the corresponding node of the next layer 
            node = node -> vecTree[c];
        }
        //  All the comparisons are finished , Indeed, one-to-one correspondence , Returns the last prefix node 
        return node;
    }
public:
    Trie() : vecTree(26), isEnd(false) {
    }   // By default, each node has 26 Child node , And not the last node 
    // Insert the function 
    void insert(string word) {
    
        //  In general, it is related to searchPrefix The same function 
        //  But when there is no prefix node , Here is a new node 
        Trie* node = this;
        for(char c : word){
    
            c = c - 'a';
            if(node -> vecTree[c] == nullptr){
    
                node -> vecTree[c] = new Trie();
            }
            node = node -> vecTree[c];
        }
        //  This is the end of the string , So make a mark , This indicates that a complete string can be formed 
        node -> isEnd = true;   // There is a string marked here 
    }
    // Lookup function , Not only through searchPrefix You can find the prefix , And this node is the last node of the string 
    // The last node here only indicates that this node can form a complete string , The point after this node will also exist isEnd = true
    bool search(string word) {
    
        Trie* node = searchPrefix(word);
        return node != nullptr && node -> isEnd;
    }
    // Find prefix function , Compared with the previous function , Just know that the prefix exists 
    bool startsWith(string prefix) {
    
        return searchPrefix(prefix) != nullptr;
    }
};

Accepted
15/15 cases passed (64 ms)
Your runtime beats 34.91 % of cpp submissions
Your memory usage beats 26.27 % of cpp submissions (47.2 MB)