ARTICLE AD BOX
I was trying to write a code for finding out the count of all such words from given input which start with a given input Prefix. For example, if my input has words 'amilie' & 'amity' & 'john' etc etc & input prefix is 'am', then the result am expecting is 2. And I have to code this problem using Trie data structure of Java. I found a Java code from Claude AI, which is giving correct result on execution. But am not able to understand one thing from this code. The code is shown below. My doubt/question is related to flag variable 'isEndOfWord'. I want to know setting this 'isEndOfWord' to true is updating value of which instance of Trie object. In this code, we are initially creating an object which is having a HashMap and a boolean flag variable as members. The HashMap has key of Character data type & value as another Trie object. Function 'insertTrieEntries' is inserting in the Trie object, all the input words which we have to check to find count of those which are starting with given input prefix. Now, as per my understanding, inside the function 'insertTriesEntries', in every iteration of the For Each loop, the object curr is updated to point to the Value of the character key inserted in that iteration. As per code, that value is always a new Trie node which is inserted in the HashMap member, as the value of the key inserted in that hashmap member, in current iteration.
Now for example, my word to be checked for prefix "am" & to be inserted in the Trie object is "amity". After the last character 'y' is inserted, the line of code curr = curr.trieEntry.get(x); will get executed & my curr reference variable starts pointing to object stored as value of key 'y'. Now that object's flag 'isEndOfWord' will be set to true right. It wont make flag variable 'isEndOfWord' of object having hashmap containing key 'y' as also true. But it seems as if the other functions in the program are working considering flag 'isEndOfWord' as true for object having hashmap containing key 'y'.
My question is to know which object/instance of Trie object gets flag 'isEndOfWord' as true, is it the object where 'y' is the key in its HashMap or the object which is stored in the value of 'y' key. In other words, I want to understand last two lines of function 'insertTrieEntries'.
import java.util.HashMap; class Tries { HashMap<Character, Tries> trieEntry = new HashMap<>(); boolean isEndOfWord = false; } public class tempTrie { static Tries root = new Tries(); String prefix = "am"; static int count = 0; public static void insertTrieEntries(String word) { Tries curr = root; for (char x : word.toCharArray()) { if (!curr.trieEntry.containsKey(x)) { curr.trieEntry.put(x, new Tries()); } curr = curr.trieEntry.get(x); } curr.isEndOfWord = true; } public static int countWordsWithPrefix(String prefix) { Tries curr = root; // Navigate to the end of the prefix in the trie for (char x : prefix.toCharArray()) { if (!curr.trieEntry.containsKey(x)) return 0; curr = curr.trieEntry.get(x); } // DFS count all words under this node return dfsCount(curr); } private static int dfsCount(Tries node) { // int count = node.isEndOfWord ? 1 : 0; // for (Tries child : node.trieEntry.values()) { // count += dfsCount(child); // } // return count; if(node.isEndOfWord) { count++; } for(Tries x: node.trieEntry.values()) { dfsCount(x); } return count; } public int checkEachWord(String[] arr) { root = new Tries(); // reset trie for (String word : arr) { insertTrieEntries(word); } return countWordsWithPrefix(prefix); } public static void main(String[] args) { tempTrie obj = new tempTrie(); String[] arr = {"amity", "amitus", "amitusq", "amitu"}; System.out.println(obj.checkEachWord(arr)); //Output : 4 } }