Interview Classic 150 Questions P208 Implement Trie (Prefix Tree)

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2025-11-24

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Trie

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Title:

P208 ImplementTrie（Prefix Tree）

https://leetcode.cn/problems/implement-trie-prefix-tree/description/?envType=study-plan-v2&envId=top-interview-150

Prefix tree implementation, note that it must have is_end to determine if it is the end of a word.
In fact, you can directly use a vector to store, because there are only 26 letters, just convert letters to numbers.

#include <string>
#include <vector>
#include <unordered_map>
using std::vector;
using std::string;
using std::unordered_map;

typedef struct TrieNode {
	//vector<struct TrieNode *> children;
	unordered_map<char, struct TrieNode *> children;
	char data;
	bool is_end;
} TrieNode;

class Trie {
    private:
	TrieNode *root;

    public:
	Trie()
	{
		root = new TrieNode;
		root->children = unordered_map<char, TrieNode *>();
		root->is_end = false;
	}

	void insert(string word)
	{
		TrieNode *p = root, *node;
		int i = 0, n = word.size();
		char ch;
		for (i = 0; i < n; i++) {
			ch = word[i];
			if (p->children.count(ch)) {
				p = p->children[ch];
				if (i == n - 1) {
					p->is_end = true;
				}
				continue;
			}

			node = new TrieNode;
			node->children = unordered_map<char, TrieNode *>();
			node->data = ch;
			if (i == n - 1) {
				node->is_end = true;
			} else {
				node->is_end = false;
			}
			p->children[ch] = node;
			p = node;
		}
	}

	bool search(string word)
	{
		int i, n = word.size();
		char ch;
		TrieNode *p = root;
		for (i = 0; i < n; i++) {
			ch = word[i];
			if (p->children.count(ch)) {
				p = p->children[ch];
				continue;
			}
			return false;
		}

		return p->is_end;
	}

	bool startsWith(string prefix)
	{
		int i, n = prefix.size();
		char ch;
		TrieNode *p = root;
		for (i = 0; i < n; i++) {
			ch = prefix[i];
			if (p->children.count(ch)) {
				p = p->children[ch];
				continue;
			}
			return false;
		}

		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);
 */

leetcode hot 100 rewrite

#include <string>
#include <vector>
using std::string;
using std::vector;

struct TrieNode {
        char val;
        vector<struct TrieNode *> children;
        bool is_end;
        TrieNode()
        {
                this->children = vector<struct TrieNode *>(26, nullptr);
        }
};

class Trie {
    private:
        TrieNode *root;

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

        void insert(string word)
        {
                TrieNode *p = root;
                for (char ch : word) {
                        if (p->children[ch - 'a'] == nullptr) {
                                p->children[ch - 'a'] = new TrieNode;
                                p->children[ch - 'a']->val = ch;
                                p->children[ch - 'a']->is_end = false;
                        }
                        p = p->children[ch - 'a'];
                }
                p->is_end = true;
        }

        bool search(string word)
        {
                TrieNode *p = root;
                for (char ch : word) {
                        if (p->children[ch - 'a'])
                                p = p->children[ch - 'a'];
                        else
                                return false;
                }
                return p->is_end;
        }

        bool startsWith(string prefix)
        {
                TrieNode *p = root;
                for (char ch : prefix) {
                        if (p->children[ch - 'a'])
                                p = p->children[ch - 'a'];
                        else
                                return false;
                }
                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);
 */