Calculating sum of squares of rectangles, which bottoms are located on one line

CalcSumSquare.kt

data class Rect(val left:Float, val right:Float, val height:Float)

data class Mark(val rect:Rect, val value:Float, val isFinish:Boolean)

fun calcSquare(data:List<Rect>):Float {
    if (data.isEmpty()) {
        return .0f
    }
    val marks = arrayListOf<Mark>()
    for (rect in data) {
        marks.add(Mark(rect, rect.left, false))
        marks.add(Mark(rect, rect.right, true))
    }
    val timelapse = marks.sortedBy { it.value }
    var square = .0f
    var cur:Float = timelapse.first().value
    val queue = PriorityQueue<Rect>({f1, f2 -> f2.height.compareTo(f1.height)} )
    queue.add(timelapse.first().rect)
    for (mark in timelapse.drop(1)) {
        val width = mark.value - cur
        val height = if (queue.isEmpty()) .0f else queue.peek().height
        square += width * height
        cur = mark.value
        if (mark.isFinish) {
            while(!queue.isEmpty() && queue.peek().right <= cur) {
                queue.poll()
            }
        } else {
            queue.add(mark.rect)
        }
    }
    return square
}