code: func (b *LRUCache) Clear() int {
  	b.lock.Lock()
  	defer b.lock.Unlock()
  
  	// First, remove entries that have expiry set
  	l := len(b.priorityQueue)
  	for i := 0; i < l; i++ {
  		// This could be reduced to O(n).
  		b.removeEntry(b.priorityQueue[0])
  	}
  
  	// Second, remove all remaining entries
  	r := b.lruList.Len()
  	for i := 0; i < r; i++ {
  		b.removeEntry(b.leastUsedEntry())
  	}
  	return l + r
  }
docs: // Evict all items from the cache. O(n*log(n))