Implement Trie (Prefix Tree)

MediumTries

Implement a trie supporting insert, search for a full word, and startsWith for a prefix.

Constraints

1 <= word.length <= 2000
Lowercase English letters

26-way children with end flag

Time O(L) per operationSpace O(total characters)

Each node holds up to 26 child links and a flag marking the end of a word. Insert walks/creates nodes; search and startsWith walk the path, with search also checking the end flag.

#include <bits/stdc++.h>
using namespace std;

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