贪心算法：活动选择问题

def solve():
    activities = [(____,____),(____,____),(____,____),(____,____),(____,____),(____,____),(____,____),(____,____),(____,____),(____,____),(____,____)]
    activities.sort(____)
    count = ____
    last_end = -____
    for start, end in activities:
        if start >= last_end:
            count += ____
            last_end = end
    print(____)