208

208. Implement Trie (Prefix Tree) (Medium)

A trie (pronounced as "try") or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker.

Implement the Trie class:

• Trie() Initializes the trie object.
• void insert(String word) Inserts the string word into the trie.
• boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
• boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.

 

Example 1:

Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output
[null, null, true, false, true, null, true]

Explanation
Trie trie = new Trie();
trie.insert("apple");
trie.search("apple");   // return True
trie.search("app");     // return False
trie.startsWith("app"); // return True
trie.insert("app");
trie.search("app");     // return True

 

Constraints:

• 1 <= word.length, prefix.length <= 2000
• word and prefix consist only of lowercase English letters.
• At most 3 * 104 calls in total will be made to insert, search, and startsWith.

Companies:
Twitter, Google, Amazon, Microsoft, Apple

Related Topics:
Hash Table, String, Design, Trie

Similar Questions:

• Design Add and Search Words Data Structure (Medium)
• Design Search Autocomplete System (Hard)
• Replace Words (Medium)
• Implement Magic Dictionary (Medium)
• Implement Trie II (Prefix Tree) (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/implement-trie-prefix-tree/
// Author: github.com/lzl124631x
// Time: O(W) for insert/search/startsWith
// Space: O(1) extra space for all
struct TrieNode {
    TrieNode* next[26] = {};
    bool end = false;
};
class Trie {
    TrieNode root;
    TrieNode *find(string &word) {
        auto n = &root;
        for (char c : word) {
            if (!n->next[c - 'a']) return nullptr;
            n = n->next[c - 'a'];
        }
        return n;
    }
public:
    void insert(string word) {
        auto n = &root;
        for (char c : word) {
            if (!n->next[c - 'a']) n->next[c - 'a'] = new TrieNode();
            n = n->next[c - 'a'];
        }
        n->end = true;
    }
    bool search(string word) {
        auto n = find(word);
        return n && n->end;
    }
    bool startsWith(string prefix) {
        return find(prefix);
    }
};