public var val: Int

public var next: ListNode?

public init(_ val: Int) {

self.val = val

self.next = nil

}

func removeElements(_ head: ListNode?, _ val: Int) -> ListNode? {

let dummy = ListNode(0)

dummy.next = head

var (pre, cur) = (dummy, head)

while cur != nil {

if cur!.val == val {

pre.next = cur!.next

} else {

pre = cur!

}

cur = cur?.next

}

return dummy.next

}