code: func (b *LRUCache) ExpireNow(now time.Time) int {
  	b.lock.Lock()
  	defer b.lock.Unlock()
  
  	i := 0
  	for {
  		e := b.expiredEntry(now)
  		if e == nil {
  			break
  		}
  		b.removeEntry(e)
  		i += 1
  	}
  	return i
  }
docs: // Evict items that expire before `now`. O(n*log(n))