1669. Merge In Between Linked Lists

/*
1669. Merge In Between Linked Lists
Runtime: 1 ms, faster than 100.00% of Java online submissions for Merge In Between Linked Lists.
Memory Usage: 42.5 MB, less than 95.86% of Java online submissions for Merge In Between Linked Lists.


*
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    
    public ListNode mergeInBetween(ListNode list1, int a, int b, ListNode list2)
    {
        int first =0;
        ListNode pointer1=list1;
        ListNode pointer2=list1;
        
        
        while(first<=b)
        {   pointer1=pointer1.next;
            first++;
        }
        
        first=0;
        while(first<a-1)
        {   pointer2=pointer2.next;
            first++;
        }
        
        
        pointer2.next=list2;
        
        while(list2.next!=null)
            list2=list2.next;
        
        list2.next=pointer1;
        
        return list1;
        
        
        
    }
}