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.
Input
["Trie", "insert", "search", "search", "startsWith", "insert", "search"]
[[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]]
Output:
[null, null, true, false, true, null, true]
Explanation:
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
class Trie {
public:
Trie() {
}
void insert(string word) {
Trie *node = this;
for(char c:word)
{
c -= 'a';
if(node->child[c] == NULL)
{
node->child[c] = new Trie();
}
node = node->child[c];
}
node->isWord = true;
}
bool search(string word) {
Trie* node = this;
for(char c:word)
{
c -= 'a';
if(node->child[c])
{
node = node->child[c];
}
else
return false;
}
return node->isWord;
}
bool startsWith(string prefix) {
Trie* node = this;
for(char c:prefix)
{
c -= 'a';
if(node->child[c])
node = node->child[c];
else
return false;
}
return true;
}
Trie *child[26] = {};
bool isWord = false;
};
/**
* 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);
*/
Complexity
Time:
insert(word): O(|word|)
search(word): O(|word|)
startsWith(prefix): O(|prefix|)
Space: O(T), where T is total of Trie nodes, in the worst case it's total number of characters of words we inserted.