package q986

import "slices"

type listElem struct {
	x       int
	listId  int8 // 0, 1
	isStart bool
}

func intervalIntersection(firstList [][]int, secondList [][]int) [][]int {
	locations := make([]listElem, 0, len(firstList)*2+len(secondList)*2)

	for i := range firstList {
		locations = append(
			locations,
			listElem{x: firstList[i][0], listId: 0, isStart: true},
			listElem{x: firstList[i][1], listId: 0, isStart: false},
		)
	}
	for i := range secondList {
		locations = append(
			locations,
			listElem{x: secondList[i][0], listId: 1, isStart: true},
			listElem{x: secondList[i][1], listId: 1, isStart: false},
		)
	}
	slices.SortFunc(locations, func(a, b listElem) int {
		if a.x != b.x {
			return a.x - b.x
		}
		if a.isStart {
			return -1
		}
		return 1
	})

	ret := [][]int{}
	start := 0
	isA, isB := false, false
	for _, loc := range locations {
		if loc.isStart {
			start = loc.x
			switch loc.listId {
			case 0:
				isA = true
			default:
				isB = true
			}
		} else {
			if isA && isB {
				ret = append(ret, []int{start, loc.x})
			}
			switch loc.listId {
			case 0:
				isA = false
			default:
				isB = false
			}
		}
	}

	return ret
}

var _ = intervalIntersection