def merge_intervals(intervals):
    if not intervals:
        return []
    sorted_intervals = sorted(([s, e] for s, e in intervals), key=lambda x: x[0])
    merged = [sorted_intervals[0][:]]
    for start, end in sorted_intervals[1:]:
        last = merged[-1]
        if start <= last[1]:
            last[1] = max(last[1], end)
        else:
            merged.append([start, end])
    return merged