Solution.swift

/** public class ListNode {
* var val: Int
* var next: ListNode?
* init(_ x: Int) {
* self.val = x
* self.next = nil
* }
* }
*/

classSolution{
func partition(_ head:ListNode?, _ x:Int)->ListNode?{
letleftDummy=ListNode(0)
letrightDummy=ListNode(0)
varleft= leftDummy
varright= rightDummy
varhead= head

whilelet current = head {
if current.val < x {
 left.next = current
 left = left.next!
}else{
 right.next = current
 right = right.next!
}
 head = head?.next
}

 right.next =nil
 left.next = rightDummy.next

return leftDummy.next
}
}