LeetCode [208] Implement Trie (Prefix Tree)

 208. Implement Trie (Prefix Tree)

Medium

Trie (we pronounce "try") or prefix tree is a tree data structure used to retrieve a key in a strings dataset. There are various applications of this very efficient data structure, such as autocomplete and spellchecker.

Implement the Trie class:

• Trie() initializes the trie object.
• void insert(String word) inserts the string word to 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 of lowercase English letters.
• At most 3 * 104 calls will be made to insert, search, and startsWith.

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class Trie { class TrieNode{ boolean isEnd; TrieNode[] children; TrieNode(){ isEnd = false; children = new TrieNode[26]; } } TrieNode root; /** Initialize your data structure here. */ public Trie() { root = new TrieNode(); } /** Inserts a word into the trie. */ public void insert(String word) { TrieNode p = root; for(char c : word.toCharArray()){ if(p.children[c-'a']==null){ p.children[c-'a'] = new TrieNode(); } p = p.children[c-'a'] ; } p.isEnd = true; } /** Returns if the word is in the trie. */ public boolean search(String word) { TrieNode p = root; for(char c : word.toCharArray()){ if(p.children[c-'a']==null){ return false; } p = p.children[c-'a'] ; } return p.isEnd == true; } /** Returns if there is any word in the trie that starts with the given prefix. */ public boolean startsWith(String prefix) { TrieNode p = root; for(char c : prefix.toCharArray()){ if(p.children[c-'a']==null){ return false; } p = p.children[c-'a'] ; } return true; } } /** * Your Trie object will be instantiated and called as such: * Trie obj = new Trie(); * obj.insert(word); * boolean param_2 = obj.search(word); * boolean param_3 = obj.startsWith(prefix); */