208. Implement Trie (Prefix Tree)

Posted on Edited on In

208. Implement Trie (Prefix Tree)

Description

Difficulty: Medium

Related Topics: Hash Table, String, Design, Trie

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:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
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.

Hints/Notes

  • 2023/10/05
  • Use a bool value to indicate if it’s the end of one word
  • If one node has been initialized then we should NOT recreate the node
  • 0x3F’s solution(checked)

Solution

Language: C++

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
class Trie {
public:
    struct TrieNode {
        bool end = false;
        TrieNode* children[26]{};
    };
    TrieNode* root;

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

    void insert(string word) {
        TrieNode* head = root;
        for (char c : word) {
            if (!head->children[c - 'a']) {
                head->children[c - 'a'] = new TrieNode();
            }
            head = head->children[c - 'a'];
        }
        head->end = true;
    }

    bool search(string word) {
        TrieNode* head = root;
        for (char c : word) {
            head = head->children[c - 'a'];
            if (!head) return false;
        }
        return head->end;;
    }

    bool startsWith(string prefix) {
        TrieNode* head = root;
        for (char c : prefix) {
            head = head->children[c - 'a'];
            if (!head) 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);
 */