mine.fs

type Building = {
    left   : int
    right  : int
    height : int
}

let buildings : Building[] = [| (* ... *) |]

let getHeight building = building.height
let getWidth  building = building.right - building.left
let getArea   building = getHeight building * getWidth building

type Op = {
    map    : Building -> int
    reduce : int -> int -> int
    zero   : int 
}

let maxHeight = {
    map    = getHeight
    reduce = (fun l r -> if l < r then l else r)
    zero   = System.Int32.MinValue
}

let minWidth = {
    map    = getWidth
    reduce = (fun l r -> if l > r then l else r)
    zero   = System.Int32.MaxValue
}

let totalArea = {
    map    = getArea
    reduce = (+)
    zero   = 0
}

let fs = [| maxHeight; minWidth; totalArea |]

let limits = 
    fs 
    |> Seq.map (fun f -> 
        buildings 
        |> Seq.map f.map
        |> Seq.fold f.reduce f.zero)
    |> Seq.toArray