leetcode 19 Remove Nth Node From End of List

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.

用两个指针p1=head, p2=head。先让p2后移n次，再同步后移至p2==Null即可。

需要注意当p2后移n次时，p2==Null的情况。

class Solution:
    # @return a ListNode
    def removeNthFromEnd(self, head, n):
        p2=head;
        while (n>0):
            p2=p2.next
            n-=1
        <span style="color:#ff0000;">if p2==None:
            return head.next</span>
        p1=head
        while p2.next:
            p1=p1.next
            p2=p2.next
        p1.next=p1.next.next
        return head