203. Remove Linked List Elements

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        if not head:
            return head
        if not head.next:
            if head.val == val:
                return None
            else:
                return head
        dummy = ListNode(0)
        dummy.next = head
        pre = dummy
        p = head
        while p:
            if p.val == val:
                pre.next = p.next
                p = p.next
            else:
                pre = p
                p = p.next
        return dummy.next

有一种很天才的做法，递归法：

class Solution(object):
    def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        if not head:
            return None
        head.next = self.removeElements(head.next, val)
        if head.val == val:
            return head.next
        else:
            return head