Monday, March 6, 2017

Remove Nth Node From End of List

Given a linked list, remove the nth node from the end of list and return its head.
For example,
   Given linked list: 1->2->3->4->5, and n = 2.

   After removing the second node from the end, the linked list becomes 1->2->3->5.
Note:
Given n will always be valid.
Try to do this in one pass.
Sol:

 public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode start = new ListNode(0);
        ListNode first=start, second=start;
        start.next = head;
     
        // Move n nodes
        for (int i=0; i<=n; i++) {
            first = first.next;
        }
        // Move both pointers one node at a time until end of list
        while(first!=null) {
           first = first.next;
           second = second.next;
        }
       
       // remove nth node from end
       second.next = second.next.next;
       return start.next;
    }

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