Remove Linked List Elements

题目：

Remove all elements from a linked list of integers that have value val.

Example

Given: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6

Return: 1 --> 2 --> 3 --> 4 --> 5
代码：
# Definition for singly-linked list.

# class ListNode:

# def __init__(self, x):

# self.val = x

# self.next = None

class Solution:

# @param {ListNode} head

# @param {integer} val

# @return {ListNode}

def removeElements(self, head, val):

sentry = ListNode(-1)

sentry.next = head

pre,tmp = sentry,head

while tmp:

if tmp.val==val:

pre.next=tmp.next

tmp = pre.next

else:

pre=pre.next

tmp=tmp.next

return sentry.next