986. Interval List Intersections

    func intervalIntersection(_ A: [Interval], _ B: [Interval]) -> [Interval] {
        var arr = A + B
        //这里由于输入都是有序的。 可以双指针loop形成sorted list
        arr.sort{
            if $0.start == $1.start {
                return $0.end < $1.end
            }
            return $0.start < $1.start
        }
        var res = [Interval]()
        var preEnd = -1
        for inter in arr{
            if inter.start <= preEnd{

                res.append(Interval(inter.start, min(inter.end, preEnd)))
                // preEnd = inter.end
            }
            preEnd = max(inter.end, preEnd)

        }




        return res
    }