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 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.
word and prefix consist only of lowercase English letters.
At most 3 * 104 calls in total will be made to insert, search, and startsWith.
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class Trie {
private TrieNode root;
/** Initialize your data structure here. */
public Trie() {
root = new TrieNode();
}
/** Inserts a word into the trie. */
public void insert(String word) {
root.insert(word, 0);
}
/** Returns if the word is in the trie. */
public boolean search(String word) {
TrieNode node = root.find(word, 0);
return node != null && node.hasWord;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
TrieNode node = root.find(prefix, 0);
return node != null;
}
}
class TrieNode {
private TrieNode[] children;
public boolean hasWord;
public TrieNode() {
children = new TrieNode[26];
hasWord = false;
}
public void insert(String word, int index) {
if (index == word.length()) {
this.hasWord = true;
return;
}
int pos = word.charAt(index) - 'a';
if (children[pos] == null) {
children[pos] = new TrieNode();
}
children[pos].insert(word, index + 1);
}
public TrieNode find(String word, int index) {
if (index == word.length()) return this;
int pos = word.charAt(index) - 'a';
if (children[pos] == null) return null;
return children[pos].find(word, index + 1);
}
}
/**
* 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);
*/
more intuitive:
class Trie {
TrieNode root;
/** Initialize your data structure here. */
public Trie() {
root = new TrieNode();
}
/** Inserts a word into the trie. */
public void insert(String word) {
TrieNode r = root;
for (int i = 0; i < word.length(); i++) {
int pos = word.charAt(i) - 'a';
if (r.next[pos] == null) r.next[pos] = new TrieNode();
r = r.next[pos];
}
r.isWord = true;
}
/** Returns if the word is in the trie. */
public boolean search(String word) {
TrieNode r = root;
for (int i = 0; i < word.length(); i++) {
int pos = word.charAt(i) - 'a';
if (r.next[pos] == null) return false;
r = r.next[pos];
}
return r.isWord;
}
/** Returns if there is any word in the trie that starts with the given prefix. */
public boolean startsWith(String prefix) {
TrieNode r = root;
for (int i = 0; i < prefix.length(); i++) {
int pos = prefix.charAt(i) - 'a';
if (r.next[pos] == null) return false;
r = r.next[pos];
}
// prefix is word
if (r.isWord) return true;
// iterate next[]
for (TrieNode t : r.next) {
if (t != null) return true;
}
return false;
}
}
class TrieNode {
TrieNode[] next;
boolean isWord;
public TrieNode() {
next = new TrieNode[26];
}
}
/**
* 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);
*/