Implement Trie (Prefix Tree)

Desicription

Implement a trie with insert, search, and startsWith methods.

Example:

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Trie trie = new Trie();
trie.insert("apple");
trie.search("apple"); // returns true
trie.search("app"); // returns false
trie.startsWith("app"); // returns true
trie.insert("app");
trie.search("app"); // returns true

Note:

  • You may assume that all inputs are consist of lowercase letters a-z.
  • All inputs are guaranteed to be non-empty strings.

Solution

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/**
* 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);
*/
class Trie {
private:
struct TrieNode {
TrieNode* next[26] = {NULL};
bool isWord = false;
};
TrieNode* find(string word) {
TrieNode* p = root;
for(int i = 0; word[i] && p; i++) {
p = p->next[word[i]-'a'];
}
return p;
}
TrieNode* root = NULL;
public:
/** Initialize your data structure here. */
Trie() {
root = new TrieNode();
}
/** Inserts a word into the trie. */
void insert(string word) {
TrieNode* p = root;
for(int i = 0; word[i]; i++) {
if(p->next[word[i]-'a'] == NULL)
p->next[word[i]-'a'] = new TrieNode();
p = p->next[word[i]-'a'];
}
p->isWord = true;
}
/** Returns if the word is in the trie. */
bool search(string word) {
TrieNode* p = find(word);
if(p == NULL || p->isWord == false)
return false;
return true;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
bool startsWith(string prefix) {
return find(prefix) != NULL;
}
};