캘린더 이벤트 겹침 처리 알고리즘

겹치는 이벤트들을 나란히 배치하기 위한 레인 할당: 시작 순으로 보며 비어 있는 가장 낮은 레인에 넣으면, 레인 수가 동시에 겹치는 최대 개수와 같아진다(구간 그래프의 탐욕 색칠).¹

interface Event {
  id: string
  start: number
  end: number
}
interface PositionedEvent extends Event {
  lane: number
  totalLanes: number
}

function calculatePositions(events: Event[]): PositionedEvent[] {
  // 1. 시작 시간 순 정렬
  const sorted = [...events].sort((a, b) => a.start - b.start || a.end - b.end)

  // 2. 겹침 그룹 찾기 + 레인 할당
  const result: PositionedEvent[] = []
  let group: Event[] = []
  let groupEnd = 0

  sorted.forEach((event) => {
    if (group.length === 0 || event.start < groupEnd) {
      group.push(event)
      groupEnd = Math.max(groupEnd, event.end)
    } else {
      processGroup(group, result)
      group = [event]
      groupEnd = event.end
    }
  })
  if (group.length) processGroup(group, result)

  return result
}

function processGroup(group: Event[], result: PositionedEvent[]) {
  const activeLanes: number[] = []

  group.forEach((event) => {
    // 사용 가능한 가장 낮은 레인 찾기
    let lane = activeLanes.findIndex((end) => end <= event.start)
    if (lane === -1) lane = activeLanes.length

    activeLanes[lane] = event.end
    result.push({ ...event, lane, totalLanes: 0 })
  })

  // totalLanes 업데이트
  const maxLane =
    Math.max(...result.slice(-group.length).map((e) => e.lane)) + 1
  result.slice(-group.length).forEach((e) => (e.totalLanes = maxLane))
}

// CSS 적용: left = lane/totalLanes * 100%, width = 100%/totalLanes

• FullCalendar
• Interval Scheduling

---

Footnotes

1. Interval graph - Wikipedia: “An optimal graph coloring of the interval graph represents an assignment of resources that covers all of the requests with as few resources as possible; it can be found in polynomial time by a greedy coloring algorithm that colors the intervals in sorted order by their left endpoints.” ↩