## 2 Literature Review  
To address the short life cycle of electronic products, warehouse management requires more effective storage planning methods. Storage location planning affects almost all key warehouse performance indicators, including order picking time and costs, production rate, shipping and inventory accuracy, and storage density [3]. The key performance indicators in warehousing are usually related to the time or workload required for order picking [4]. [PERSON] and [PERSON] [5] proposed four aspects of reducing the distance and time required for order picking activities, i.e., order picking path, warehouse partitioning planning, storage location planning, and batch picking. Storage location planning is used to allocate materials to the correct storage location. Appropriate storage location planning can effectively reduce the order picking distance and time than the other three aspects [6]. Because storage location planning directly affects order picking performance. Therefore, this iterative relationship between storage location planning and picking operations must be considered in the design stage of warehouse planning [7]. Accordingly, the optimization of storage location planning is the primary consideration in this study, and then picking list clustering is performed to increase picking efficiency. The different methods of storage location planning are introduced, classified, and discussed. Storage location planning ways are divided into two main types: the dedicated storage way and the shared storage way. The dedicated storage way allocates specific items to fixed storage locations and is more commonly implemented in manually managed warehouses. In dedicated storage, when the inventory space for the specific items is full, these items cannot be stored in other empty storage spaces. Therefore, to improve the utilization of storage space, scholars proposed a shared storage way that allows any item to be allocated to an empty storage location. Warehouses that implement the shared storage way must be managed by a computer system to accurately track the location of the items. The shared storage way is divided into the random storage method and the classified storage method. When a random storage method is adopted, storage-location information is required during the receiving and pick-up operation of items [8]. The classified storage method is based on the logic of dedicated storage and eliminates the need for detailed and accurate tracking of the items' locations and other tedious tasks [9]. Thus, the classified storage method classifies items in accordance with the appropriate standards; then, storage locations are conveniently allocated with the random storage method. [PERSON] et al. [10] described three commonly used storage location planning policies: the haphazard storage policy, the dedicated storage policy, and the class-based storage policy. The haphazard storage policy can result in the longest order picking distance but requires the minimum warehouse space. The dedicated storage policy yields the shortest order picking distance but the lowest warehouse space utilization. If the demand for the product changes, the optimal storage location of the product is affected, which necessitates a readjustment of the storage location and in turn, causes substantial increases in maintenance costs. By contrast, the average order picking distance in the class-based storage policy is between that of the haphazard and dedicated storage policies [11]. Because class-based storage offers the flexibility to respond to changes in classification methods and order picking frequency, it is the widely used method in practice. The class-based storage method is a compromise between the dedicated and haphazard storage methods. [PERSON] and [PERSON] [12] noted that in the class-based storage method, random arrangement of the locations of the materials in each class can improve the utilization of space and shorten order picking time. Sorting materials on the basis of turnover is the most common method of classification.