刪除整數連結串列中值為val的節點

Example:

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

1：簡單判斷節點值與val是否相等，並對判斷結果執行對應的操作

def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        while head is not None and head.val==val:    #保證連結串列第一個節點的值不等於val
            head=head.next
        if not head:         #判斷連結串列是否為空
            return None
        headNode = head     #頭節點
        while head.next is not None:
            if head.next.val==val:
                head.next = head.next.next
            else:
                head=head.next
        return headNode
 

另一種寫法（參考他人程式碼）

def removeElements(self, head, val):
        """
        :type head: ListNode
        :type val: int
        :rtype: ListNode
        """
        if not head:
            return None
        headNode = ListNode(1)   #頭節點
        headNode.next = head
        preNode = headNode    #當前節點的上一個節點
        cur = headNode.next   #當前節點
        while cur is not None:
            if cur.val==val:
                preNode.next = cur.next
                cur = preNode.next
            else:
                preNode = preNode.next
                cur = cur.next
        return headNode.next