shorter.fs

type OpenInterval = {Start: int; End: int }

let sorted = [{Start = 10; End = 19};
              {Start = 11; End = 19};
              {Start = 0; End = 8}] |> Seq.sortBy (fun f -> f.Start) 

let stack = new Stack<OpenInterval>()
stack.Push (Seq.head sorted)

for interval in Seq.tail sorted do
    let overLap i i' = i.End + 1 >= i'.Start
    if not (overLap (stack.Peek()) interval) then
        stack.Push interval       
    else if (overLap (stack.Peek()) interval) && interval.End > (stack.Peek()).End then        
        stack.Push({ (stack.Pop()) with End = interval.End })

stack.Sum(System.Func<OpenInterval,int>(fun i -> i.End - i.Start)) |> printf "%A"