11package com .thealgorithms .datastructures .trees ;
22
3+ import java .util .HashMap ;
4+
5+ /**
6+ * Represents a Trie Node that stores a character and pointers to its children.
7+ * Each node has a hashmap which can point to all possible characters.
8+ * Each node also has a boolean value to indicate if it is the end of a word.
9+ */
10+ class TrieNode {
11+ char value ;
12+ HashMap <Character , TrieNode > child ;
13+ boolean end ;
14+
15+ /**
16+ * Constructor to initialize a TrieNode with an empty hashmap
17+ * and set end to false.
18+ */
19+ TrieNode (char value ) {
20+ this .value = value ;
21+ this .child = new HashMap <>();
22+ this .end = false ;
23+ }
24+ }
25+
326/**
427 * Trie Data structure implementation without any libraries.
528 * <p>
1437 * possible character.
1538 *
1639 * @author <a href="https://github.com/dheeraj92">Dheeraj Kumar Barnwal</a>
40+ * @author <a href="https://github.com/sailok">Sailok Chinta</a>
1741 */
18- public class TrieImp {
1942
20- /**
21- * Represents a Trie Node that stores a character and pointers to its children.
22- * Each node has an array of 26 children (one for each letter from 'a' to 'z').
23- */
24- public class TrieNode {
25-
26- TrieNode [] child ;
27- boolean end ;
28-
29- /**
30- * Constructor to initialize a TrieNode with an empty child array
31- * and set end to false.
32- */
33- public TrieNode () {
34- child = new TrieNode [26 ];
35- end = false ;
36- }
37- }
43+ public class Trie {
44+ private static final char ROOT_NODE_VALUE = '*' ;
3845
3946 private final TrieNode root ;
4047
4148 /**
4249 * Constructor to initialize the Trie.
4350 * The root node is created but doesn't represent any character.
4451 */
45- public TrieImp () {
46- root = new TrieNode ();
52+ public Trie () {
53+ root = new TrieNode (ROOT_NODE_VALUE );
4754 }
4855
4956 /**
@@ -57,13 +64,15 @@ public TrieImp() {
5764 public void insert (String word ) {
5865 TrieNode currentNode = root ;
5966 for (int i = 0 ; i < word .length (); i ++) {
60- TrieNode node = currentNode .child [word .charAt (i ) - 'a' ];
67+ TrieNode node = currentNode .child .getOrDefault (word .charAt (i ), null );
68+
6169 if (node == null ) {
62- node = new TrieNode ();
63- currentNode .child [ word .charAt (i ) - 'a' ] = node ;
70+ node = new TrieNode (word . charAt ( i ) );
71+ currentNode .child . put ( word .charAt (i ), node ) ;
6472 }
6573 currentNode = node ;
6674 }
75+
6776 currentNode .end = true ;
6877 }
6978
@@ -80,13 +89,14 @@ public void insert(String word) {
8089 public boolean search (String word ) {
8190 TrieNode currentNode = root ;
8291 for (int i = 0 ; i < word .length (); i ++) {
83- char ch = word .charAt (i );
84- TrieNode node = currentNode . child [ ch - 'a' ];
92+ TrieNode node = currentNode . child . getOrDefault ( word .charAt (i ), null );
93+
8594 if (node == null ) {
8695 return false ;
8796 }
8897 currentNode = node ;
8998 }
99+
90100 return currentNode .end ;
91101 }
92102
@@ -104,40 +114,89 @@ public boolean search(String word) {
104114 public boolean delete (String word ) {
105115 TrieNode currentNode = root ;
106116 for (int i = 0 ; i < word .length (); i ++) {
107- char ch = word .charAt (i );
108- TrieNode node = currentNode .child [ch - 'a' ];
117+ TrieNode node = currentNode .child .getOrDefault (word .charAt (i ), null );
109118 if (node == null ) {
110119 return false ;
111120 }
121+
112122 currentNode = node ;
113123 }
124+
114125 if (currentNode .end ) {
115126 currentNode .end = false ;
116127 return true ;
117128 }
129+
118130 return false ;
119131 }
120132
121133 /**
122- * Helper method to print a string to the console.
134+ * Counts the number of words in the trie
135+ *<p>
136+ * The method traverses the Trie and counts the number of words.
123137 *
124- * @param print The string to be printed.
138+ * @return count of words
125139 */
126- public static void sop (String print ) {
127- System .out .println (print );
140+ public int countWords () {
141+ return countWords (root );
142+ }
143+
144+ private int countWords (TrieNode node ) {
145+ if (node == null ) {
146+ return 0 ;
147+ }
148+
149+ int count = 0 ;
150+ if (node .end ) {
151+ count ++;
152+ }
153+
154+ for (TrieNode child : node .child .values ()) {
155+ count += countWords (child );
156+ }
157+
158+ return count ;
128159 }
129160
130161 /**
131- * Validates if a given word contains only lowercase alphabetic characters
132- * (a-z).
133- * <p>
134- * The method uses a regular expression to check if the word matches the pattern
135- * of only lowercase letters.
162+ * Check if the prefix exists in the trie
136163 *
137- * @param word The word to be validated.
138- * @return true if the word is valid (only a-z), false otherwise.
164+ * @param prefix the prefix to be checked in the Trie
165+ * @return true / false depending on the prefix if exists in the Trie
139166 */
140- public static boolean isValid (String word ) {
141- return word .matches ("^[a-z]+$" );
167+ public boolean startsWithPrefix (String prefix ) {
168+ TrieNode currentNode = root ;
169+
170+ for (int i = 0 ; i < prefix .length (); i ++) {
171+ TrieNode node = currentNode .child .getOrDefault (prefix .charAt (i ), null );
172+ if (node == null ) {
173+ return false ;
174+ }
175+
176+ currentNode = node ;
177+ }
178+
179+ return true ;
180+ }
181+
182+ /**
183+ * Count the number of words starting with the given prefix in the trie
184+ *
185+ * @param prefix the prefix to be checked in the Trie
186+ * @return count of words
187+ */
188+ public int countWordsWithPrefix (String prefix ) {
189+ TrieNode currentNode = root ;
190+
191+ for (int i = 0 ; i < prefix .length (); i ++) {
192+ TrieNode node = currentNode .child .getOrDefault (prefix .charAt (i ), null );
193+ if (node == null ) {
194+ return 0 ;
195+ }
196+
197+ currentNode = node ;
198+ }
199+
200+ return countWords (currentNode );
142201 }
143202}
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