19. Remove Nth Node From End of List

problem statement

Solved

Medium

Topics

Companies

Hint

Given the head of a linked list, remove the nth node from the end of the list and return its head.

Example 1:

Input: head = [1,2,3,4,5], n = 2
Output: [1,2,3,5]

Example 2:

Input: head = [1], n = 1
Output: []

Example 3:

Input: head = [1,2], n = 1
Output: [1]

Constraints:

• The number of nodes in the list is sz.
• 1 <= sz <= 30
• 0 <= Node.val <= 100
• 1 <= n <= sz

Follow up: Could you do this in one pass?

class Solution {
    /**
    1.traverse the list and take the length of the list:
       if the element from last is k, then from the fist it will be 
       n-k shoud be pointed to next pointer of the next
       if we are dealing with head if we want to remove the head then the difference is 0 ()p)

       Time : O(n)
       Space : O(1)
    
     */
    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode t=head;
        int l=0;

        while(t!=null) {l++; t=t.next;} 
       
        int p=l-n; 

        t=head;
        for(int i=1;i<p;i++) t=t.next;
        
        if(t.next!=null && p!=0)  t.next=t.next.next;
        
        if(p==0) head= (head.next!=null) ? head.next : null;
        return head;
    }
}