#### QUESTION:

You are given the head of a linked list.

Remove every node which has a node with a strictly greater value anywhere to the right side of it.

Return the head of the modified linked list.

**Example 1:**

```
Input: head = [5,2,13,3,8]
Output: [13,8]
Explanation: The nodes that should be removed are 5, 2 and 3.
- Node 13 is to the right of node 5.
- Node 13 is to the right of node 2.
- Node 8 is to the right of node 3.
```

**Example 2:**

```
Input: head = [1,1,1,1]
Output: [1,1,1,1]
Explanation: Every node has value 1, so no nodes are removed.
```

**Constraints:**

```
The number of the nodes in the given list is in the range [1, 105].
1 <= Node.val <= 105
```

#### EXPLANATION:

#### SOLUTION:

```
/**
* Definition for singly-linked list.
* public class ListNode {
* public var val: Int
* public var next: ListNode?
* public init() { self.val = 0; self.next = nil; }
* public init(_ val: Int) { self.val = val; self.next = nil; }
* public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
* }
*/
class Solution {
func removeNodes(_ head: ListNode?) -> ListNode? {
guard let head = head else { return nil }
head.next = removeNodes(head.next)
return head != nil && head.next != nil && head.val < head.next!.val ? head.next : head
}
}
```