【LeetCode】19. Remove Nth Node From End of List

Difficulty: Medium

 More:【目錄】LeetCode Java實現

Description

https://leetcode.com/problems/remove-nth-node-from-end-of-list/

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

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.

Follow up:

Could you do this in one pass?

Intuition

Using a dummyHead.

 

Solution

    public ListNode removeNthFromEnd(ListNode head, int n) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode n0 = head;
        ListNode n1 = head;
        ListNode pre = dummy;
        for(int i=0; i<n-1; i++)
            n1=n1.next;
        while(n1.next!=null){
            n0=n0.next;
            n1=n1.next;
            pre=pre.next;
        }
        pre.next = n0.next;
        return dummy.next;  //not head
    }

　　

Complexity

Time complexity : O(n)

Space complexity : O(1)

 

 

 More:【目錄】LeetCode Java實現