Max difference between increasing elemets

MaxDiff.scala

 import Math.*

 def maxDiff(xs: List[Int]): Int = 
    xs.scanLeft(Int.MaxValue)(min)
        .tail
        .zip(xs)
        .map(x => x._2 - x._1)
        .filter(_ > 0)
        .fold(-1)(max)       

maxDiff(List(7, 1, 5, 4)) // 4
maxDiff(List(8, 5, 3 ,3)) // -1