CODEWITHSUNDEEP
javadata-structureslinked-listhashmap
Aayush Saini
Aayush Saini

Reputation: 197

How to update the nodes in the hash Map in specific key in java?

I want to remove all even nodes from the linked list. How can I update the node in the specific key of the hashmap? H.get(0).next=temp is not working. The desired output is 2 4, but I'm not getting it.

public static void main(String[] args) {
    head = new Node(1);
    head.next = new Node(2);
    head.next.next = new Node(3);
    head.next.next.next = new Node(4);
    head.next.next.next.next = new Node(5);
    Node temp=head;
    HashMap<Integer,Node>H=new HashMap<>();
        while(temp!=null) {
            if(temp.data%2==0) {
                if(!H.containsKey(0)) {
                    H.put(0, temp);
                } else {
                    //This statement is not working
                    H.get(0).next=temp;  
                }
            }
        temp=temp.next;
        }
        head=H.get(0);
        while(temp!=null) {
            System.out.print(temp.data);
            temp=temp.next;
    
        }
    }
}

Upvotes: 0

Views: 187

Answers (2)

Most Noble Rabbit
Most Noble Rabbit

Reputation: 2776

  • In the last loop, you wrote while(temp!=null){ but the temp is null after the loop and doesn't reference the head.
  • I don't see the value in using HashMap here.

Here's what we can do to remove all nodes with even data:

Node head;
head = new Node(1);
head.next = new Node(2);
head.next.next = new Node(3);
head.next.next.next = new Node(4);
head.next.next.next.next = new Node(5);

Node oddTail = null, curr = head;

while (curr != null) {
    if (curr.data % 2 != 0) { // Odd data
        if(oddTail != null){
            oddTail.next = curr; // Update oddTail
        }

        oddTail = curr;
    }

    curr = curr.next;
}

if(oddTail != null){ // The oddTail.next might point to a node with even data
    oddTail.next = null; 
} else{
    head = null; // No nodes with odd data
}

curr = head;

// Print the list
while(curr != null){
    System.out.println(curr.data);
    curr = curr.next;
}

Output:

1
3
5

Upvotes: 1

Jose Romero
Jose Romero

Reputation: 569

Normally you don't need a HashMap when doing operations on a Linked List, you just have to keep the reference of the nodes and remove them accordingly. I think something like this should work.

As you see I don't have the referenced stored in a HashMap but what I try to do is to explore from the head to the tail, keeping a reference of the previous node I explored. Why? Because when I find an even node I want to be connect the previous node to the next one such that I remove the current node. I have the edge case of when the even node is the head because there is no previous node assigned.

Wasn't really able to try this code but maybe works as a reference for what you're trying to do.

public static void main(String[] args) {
    head=new Node(1);
    head.next=new Node(2);
    head.next.next=new Node(3);
    head.next.next.next=new Node(4);
    head.next.next.next.next=new Node(5);

    Node current = head;
    Node prev = null;
    while(current != null){
        if(current.data%2==0){
            if(current == head){
              head = current.next;
            } else {
              prev.next = current.next;
              current = current.next;
            }
        } else {
            prev = current;
            current = current.next;
        }
    }
    
    current = head
    while(current!=null){
        System.out.print(current.data);
        current=current.next;
    }
}

Upvotes: 1

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