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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.

 

大概思路:

1)用p,q两个指针来记录2个位置,p,q初始化为head;

2)然后p先不动,q向后移动n个位置;

3)接着p,q以同样的步伐一起向链表尾部移动,直到q到达链表尾部,即q.next==null;

4)此时p是待删除节点的前驱,修改p.next即可。

这里一个细节要考虑,若n等于节点数,即删除倒数第n个也就是第1个节点,那么在第2)步q会移动到尾部节点下一个位置即q==null,所以移动时加个判断即可。

 

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode removeNthFromEnd(ListNode head, int n) {        ListNode p = head;        ListNode q = head;        while(n!=0){            q = q.next;            //如果q==null说明n==List.length,即删除第一个节点            if(q==null){                return head.next;            }            n--;        }        while(q.next!=null){            p = p.next;            q = q.next;        }        ListNode temp = p.next;        p.next = temp.next;        return head;    }}

 

Remove Nth Node From End of List