Q21 PepCoding | Segregate 01 Node Of Linkedlist Over Swapping Nodes

import java.util.*;

class Main {
    public static Scanner scn = new Scanner(System.in);

    public static class ListNode {
        int val = 0;
        ListNode next = null;

        ListNode(int val) {
            this.val = val;
        }
    }
    

    public static ListNode segregate01(ListNode head) {
        if(head == null || head.next == null) return head;
        
        ListNode curr = head;
        
        ListNode dummyhead = new ListNode(-1);
        ListNode zero = dummyhead;
        
        ListNode one  = new ListNode(-1);
        ListNode help = one;
        
        while(curr!=null){
            
            if(curr.val == 0){
                zero.next = curr;
                zero = zero.next;
            }
            else{
                help.next = curr;
                help = curr;
            }
                    
            curr = curr.next;
        }
        
        zero.next = one.next;
        
        return dummyhead.next;
    }

    public static void printList(ListNode node) {
        while (node != null) {
            System.out.print(node.val + " ");
            node = node.next;
        }
    }

    public static ListNode createList(int n) {
        ListNode dummy = new ListNode(-1);
        ListNode prev = dummy;
        while (n-- > 0) {
            prev.next = new ListNode(scn.nextInt());
            prev = prev.next;
        }

        return dummy.next;
    }

    public static void main(String[] args) {
        int n = scn.nextInt();
        ListNode h1 = createList(n);
        h1 = segregate01(h1);
        printList(h1);
    }
}