LeetCode-in-All

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.

Solution

% Initialize the trie using ETS
-spec trie_init_() -> any().
trie_init_() ->
    % Create ETS table if it doesn't exist
    case ets:info(trie_table) of
        undefined ->
            ets:new(trie_table, [set, public, named_table]);
        _ ->
            ets:delete(trie_table),
            ets:new(trie_table, [set, public, named_table])
    end.

% Insert a word into the trie
-spec trie_insert(Word :: unicode:unicode_binary()) -> any().
trie_insert(Word) ->
    % Insert all prefixes with false flag
    insert_prefixes(Word),
    % Mark the complete word with true flag
    ets:insert(trie_table, {Word, true}).

% Search for a complete word
-spec trie_search(Word :: unicode:unicode_binary()) -> boolean().
trie_search(Word) ->
    case ets:lookup(trie_table, Word) of
        [{_, true}] -> true;
        _ -> false
    end.

% Check if any word starts with the given prefix
-spec trie_starts_with(Prefix :: unicode:unicode_binary()) -> boolean().
trie_starts_with(Prefix) ->
    case ets:lookup(trie_table, Prefix) of
        [{_, _}] -> true;
        [] -> false
    end.

% Helper function to insert all prefixes of a word
-spec insert_prefixes(Word :: unicode:unicode_binary()) -> ok.
insert_prefixes(Word) ->
    Prefixes = get_all_prefixes(Word),
    [ets:insert_new(trie_table, {Prefix, false}) || Prefix <- Prefixes],`
    ok.

% Helper function to generate all prefixes of a word
-spec get_all_prefixes(Word :: unicode:unicode_binary()) -> [unicode:unicode_binary()].
get_all_prefixes(Word) ->
    Size = byte_size(Word),
    [binary:part(Word, 0, Len) || Len <- lists:seq(1, Size - 1)].

%% Your functions will be called as such:
%% trie_init_(),
%% trie_insert(Word),
%% Param_2 = trie_search(Word),
%% Param_3 = trie_starts_with(Prefix),

%% trie_init_ will be called before every test case, in which you can do some necessary initializations.

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