Link to the problem

The problem is here: https://leetcode-cn.com/problems/implement-trie-prefix-tree/

Trie

A trie (sounds like ‘try’), also called digital tree or prefix tree, is a type of multi-way search tree (多路搜索树).

Trie can be used in tasks like auto-complete or spell-checking.

It is used to store and search strings efficiently. An intuitive design of a trie is like this:

The root node is actually a dummy node. The boolean value of a node is indicating whether that node is a termination or not.

For example, an is a word in the trie while na is not.

Simple Implementation

class Trie {
private:
    struct TrieNode {
        vector<TrieNode *> child_;
        bool terminated_;
        TrieNode() : child_(26, nullptr), terminated_(false) { }
    };
    TrieNode root_;
public:
    /** Initialize your data structure here. */
    Trie() {}
    /** Inserts a word into the trie. */
    void insert(string word) {
        auto node = &root_;
        for (char c : word) {
            auto idx = c - 'a';
            if (!node->child_[idx]) {
                node->child_[idx] = new TrieNode();
            }
            node = node->child_[idx];
        }
        node->terminated_ = true;
    }
    /** Returns if the word is in the trie. */
    bool search(string word) {
        auto node = &root_;
        for (char c : word) {
            auto idx = c - 'a';
            if (!node->child_[idx]) {
                return false;
            }
            node = node->child_[idx];
        }
        return node->terminated_;
    }
    /** Returns if there is any word in the trie that starts with the given prefix. */
    bool startsWith(string prefix) {
        auto node = &root_;
        for (char c : prefix) {
            auto idx = c - 'a';
            if (!node->child_[idx]) {
                return false;
            }
            node = node->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);
 */

Possible Improvements

May use map instead of vector to save memory usage.