Gộp Các KhoảngMerge Intervals

function mergeNaive(intervals: number[][]): number[][] {
  const used = new Array(intervals.length).fill(false)
  const result: number[][] = []
  for (let i = 0; i < intervals.length; i++) {
    if (used[i]) continue
    let [start, end] = intervals[i]
    let changed = true
    while (changed) {           // quét lại toàn bộ tìm khoảng chồng để gộp
      changed = false
      for (let j = 0; j < intervals.length; j++) {
        if (used[j] || j === i) continue
        const [s, e] = intervals[j]
        if (s <= end && start <= e) {
          start = Math.min(start, s); end = Math.max(end, e)
          used[j] = true; changed = true
        }
      }
    }
    result.push([start, end])
  }
  return result
}