I am new to programming in Java , I had written code for trie to store numbers as bits(the last 31 bits from right) . Therefore each node has only two possible children at max, 0 or 1.
The node for each trie node has the following attributes
- Node next[] : array of size 2 pointing to next node
- int visCnt : Number of times a node has been visited, this will be
used to later delete the node ( check remove function below) - int number : the number stored at leaf node , for ex., if we insert 5 to trie, the leaf node will have value of 'number' as 5 meanwhile all other nodes from root till leaf will have default val of -1
The functions that i have implemented are
- void insert(int num) : insert 'num' to global trie
- void remove(int num, Node A,int ind) : recursive function to delete a number if it exists in global trie. For node A , I pass the root(of global trie) from the main, and reach the node to be delete. From the leaf, nodes are deleted bottom up , by checking value of visCnt.
- boolean isExist(int num) : To check if num exists in global trie
The remove function in the implementation doesn't work as expected, I have pasted the code down below for reference, (you can try running on a site like onlineGDB where it will work fine). In the main function after i insert(4) and then remove(4) i expect isExist(4) to return false but this is not the case and it returns as true. Does setting the node object as null not delete the node ?
Code:
import java.util.*;
import java.lang.*;
import java.io.*;
public class Main
{
static class Node{
Node next[] = new Node[2];
int visCnt=0;
int number = -1;
}
static Node root = new Node();
void insert(int num){
System.out.println("added "+num);
Node cur =root;
for(int i = 30;i>=0;i--){
cur.visCnt++;
int tmp = 1<<i;
int curBit = ((tmp&num)==0)?0:1;
if(cur.next[curBit]==null)
cur.next[curBit] = new Node();
cur=cur.next[curBit];
}
cur.visCnt++;
cur.number = num;
}
void remove(int num, Node A,int ind){
if(A==null){
System.out.println("removed "+num);
return;
}
A.visCnt--;
int curBit = ((1<<ind)&num)==0?0:1;
remove(num,A.next[curBit],ind-1);
if(A.visCnt==0){
A=null;
}
}
boolean isExist(int num){
System.out.println("checking for "+num);
Node cur =root;
for(int i = 30;i>=0;i--){
cur.visCnt++;
int tmp = 1<<i;
int curBit = ((tmp&num)==0)?0:1;
if(cur.next[curBit]==null){
System.out.println(num+ " does not exist in trie ");
return false;
}
cur=cur.next[curBit];
}
System.out.println(cur.number+ " exists in trie ");
return true;
}
public static void main(String[] args) {
Main trie = new Main();
trie.root.visCnt++;
trie.insert(1);
trie.insert(2);
trie.insert(4);
trie.remove(4,root,30);
trie.isExist(4);
// return ans;
}
}
Ouput
added 1
added 2
added 4
removed 4
checking for 4
4 exists in trie
