A (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 wordinto the trie.
int countWordsEqualTo(String word) Returns the number of instances of the string word in the trie.
int countWordsStartingWith(String prefix)Returns the number of strings in the trie that have the string prefix as a prefix.
void erase(String word) Erases the string wordfrom the trie.
Example 1:
Input
["Trie", "insert", "insert", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsStartingWith"]
[[], ["apple"], ["apple"], ["apple"], ["app"], ["apple"], ["apple"], ["app"], ["apple"], ["app"]]
Output
[null, null, null, 2, 2, null, 1, 1, null, 0]
Explanation
Trie trie = new Trie();
trie.insert("apple"); // Inserts "apple".
trie.insert("apple"); // Inserts another "apple".
trie.countWordsEqualTo("apple"); // There are two instances of "apple" so return 2.
trie.countWordsStartingWith("app"); // "app" is a prefix of "apple" so return 2.
trie.erase("apple"); // Erases one "apple".
trie.countWordsEqualTo("apple"); // Now there is only one instance of "apple" so return 1.
trie.countWordsStartingWith("app"); // return 1
trie.erase("apple"); // Erases "apple". Now the trie is empty.
trie.countWordsStartingWith("app"); // return 0
Constraints:
1 <= word.length, prefix.length <= 2000
word and prefix consist only of lowercase English letters.
At most 3 * 10^4 calls in total will be made to insert, countWordsEqualTo, countWordsStartingWith, and erase.
It is guaranteed that for any function call to erase, the string word will exist in the trie.
Solution
class Trie {
struct TrieNode {
TrieNode* nodes[26];
int word_cnt;
int prefix_cnt;
// Initialize your data structure here.
TrieNode() {
memset(nodes, 0, sizeof(nodes));
word_cnt = 0;
prefix_cnt = 0;
}
};
TrieNode* root;
public:
Trie() {
root = new TrieNode();
}
void insert(string word) {
TrieNode* tmp = root;
for(char ch : word) {
int index = ch - 'a';
if(tmp->nodes[index] == nullptr) {
tmp->nodes[index] = new TrieNode();
}
tmp = tmp->nodes[index];
tmp->prefix_cnt++;
}
tmp->word_cnt++;
}
int countWordsEqualTo(string word) {
TrieNode* tmp = root;
for(char ch : word) {
int index = ch - 'a';
if(tmp->nodes[index] == nullptr) {
return 0;
}
tmp = tmp->nodes[index];
}
return tmp->word_cnt;
}
int countWordsStartingWith(string prefix) {
TrieNode* tmp = root;
for(char ch : prefix) {
int index = ch - 'a';
if(tmp->nodes[index] == nullptr) {
return 0;
}
tmp = tmp->nodes[index];
}
return tmp->prefix_cnt;
}
void erase(string word) {
TrieNode* tmp = root;
TrieNode* to_be_deleted = nullptr;
for(char ch : word) {
int index = ch - 'a';
TrieNode* parent = tmp;
tmp = tmp->nodes[index];
tmp->prefix_cnt--;
if (to_be_deleted != nullptr) {
delete to_be_deleted;
}
if (tmp->prefix_cnt == 0) {
if (to_be_deleted == nullptr) {
parent->nodes[index] = nullptr;
}
to_be_deleted = tmp;
}
}
tmp->word_cnt--;
if (to_be_deleted != nullptr) {
delete to_be_deleted;
}
}
};
/**
* Your Trie object will be instantiated and called as such:
* Trie* obj = new Trie();
* obj->insert(word);
* int param_2 = obj->countWordsEqualTo(word);
* int param_3 = obj->countWordsStartingWith(prefix);
* obj->erase(word);
*/