19. 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.

Solution:

Tips:

two pointers, one pointer goes first, and then the other goes after the first pointer's N steps.

Java Code:

/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
public class Solution {
public ListNode removeNthFromEnd(ListNode head, int n) {
if (head == null) {
return head;
}

ListNode tmpNode = head;
ListNode tmpNodeNth = head;
while ((n--) > 0) {
tmpNodeNth = tmpNodeNth.next;
}
if (tmpNodeNth == null) {
return head.next;
}

tmpNodeNth = tmpNodeNth.next;
while (tmpNodeNth != null) {
tmpNodeNth = tmpNodeNth.next;
tmpNode = tmpNode.next;
}
tmpNode.next = tmpNode.next.next;

return head;
}
}