package q84

func largestRectangleArea(heights []int) int {
	var largest int
	st := make([][2]int, 0, 256) // x index, height

	for x, h := range heights {
		minX := x
		for len(st) > 0 && st[len(st)-1][1] > h {
			largest = max(largest, st[len(st)-1][1]*(x-st[len(st)-1][0]))
			minX = min(minX, st[len(st)-1][0])
			st = st[:len(st)-1]
		}

		if len(st) > 0 && st[len(st)-1][1] == h {
			continue
		}
		st = append(st, [2]int{minX, h})
	}

	for i := range st {
		x, h := st[i][0], st[i][1]
		largest = max(largest, h*(len(heights)-x))
	}

	return largest
}

var _ = largestRectangleArea