trie.cpp

#include <algorithm>
#include <iostream>
#include <string>
using namespace std;

class TrieNode {
public:
    // Initialize your data structure here.
    TrieNode(): end(false) {
        fill_n(node, 26, nullptr);
    }
    TrieNode* node[26];
    bool end;
};

class Trie {
public:
    Trie() {
        root = new TrieNode();
    }

    // Inserts a word into the trie.
    void insert(string word) {
        TrieNode* current = root;
        for (size_t i = 0; i < word.size(); i++) {
            if ((current->node)[word[i] - 'a'] == NULL) {
                (current->node)[word[i] - 'a'] = new TrieNode();
            }
            current = (current->node)[word[i] - 'a'];
        }
        current->end = true;
        return;
    }

    // Returns if the word is in the trie.
    bool search(string word) {
        TrieNode* current = root;
        for (size_t i = 0; i < word.length(); i++) {
            if ((current->node)[word[i] - 'a'] == NULL) {
                return false;
            }
            current = (current->node)[word[i] - 'a'];
        }
        return current->end;
    }

    // Returns if there is any word in the trie
    // that starts with the given prefix.
    bool startsWith(string prefix) {
        TrieNode* current = root;
        for (size_t i = 0; i < prefix.length(); i++) {
            if ((current->node)[prefix[i] - 'a'] == NULL) {
                return false;
            }
            current = (current->node)[prefix[i] - 'a'];
        }
        return true;
    }

private:
    TrieNode* root;
};

int main() {
    Trie trie;
    trie.insert("key");
    if (trie.search("key")) {
        cout << "found" << endl;
    } else {
        cout << "not found" << endl;
    }    
}