Codingame Solution: Stock Exchange Losses

Original Problem

The Goal

Game Input

VB.net Solution

Based on the first point p we got, we subtract the second point q. If q is smaller than p, we have a loss. What we now must do is maximizing the loss, so we'll go from point to point and compare the currently highest point p with every new point q. Since we can find a new high with every new point we get, we also have to maximize p. I thought visually about this problem. Look at this graph:

Imagine, you put a straight line between the first and the second point. Now you keep the first point fixed as an anker and rotate the line to the third point. That one is higher than the second, and as such the loss is less than the already known. Now we have a new high and let the third point be the anker and go down to the fourth and fifth. We now found a new maximum loss. With the next point we have to move the anker point again and the game goes on. When implemented, it's as simple as the following VB.net snippet:

Module Solution

    Sub Main ()

        Dim n as Integer
        n = Console.ReadLine()

        Dim vs(n) as String
        vs = Console.ReadLine().split(" ")

        Dim p as Integer
        Dim d as Integer

        p = Convert.toInt32(vs(0))
        d = 0

        For Each v As String In vs
            Dim t as Integer

            t = Convert.toInt32(v)
            d = Math.max(d, p - t) ' max loss
            p = Math.max(p, t) ' max seen value
        Next

        Console.WriteLine(- d)

    End Sub
End Module

It's also possible to reverse the idea so that the negation at the end isn't necessary:

Module Solution

Sub Main ()

    Dim n as Integer
    n = Console.ReadLine()

    Dim vs(n) as String
    vs = Console.ReadLine().split(" ")

    Dim p as Integer
    Dim d as Integer

    p = Convert.toInt32(vs(0))
    d = 0

    For Each v As String In vs
        Dim t as Integer

        t = Convert.toInt32(v)
        d = Math.min(d, t - p) ' max loss
        p = Math.max(p, t) ' max seen value
    Next

    Console.WriteLine(d)

End Sub
End Module