def merge_intervals(intervals):
    if not intervals:
        return []

    sorted_intervals = sorted(intervals, key=lambda interval: (interval[0], interval[1]))
    merged = []

    for start, end in sorted_intervals:
        if not merged or start > merged[-1][1]:
            merged.append([start, end])
        elif end > merged[-1][1]:
            merged[-1][1] = end

    return merged