For efficient data retrieval, when is it recommended to use a hashed table?

Using a hashed table is recommended when the complete key is known as it allows for extremely efficient data retrieval. Hashed tables utilize a hash algorithm to map keys directly to their corresponding values, which minimizes the search time for looking up entries. This means that when the complete key is available, the system can quickly compute the hash and access the data without having to scan through other entries.

The efficiency of hashed tables comes from their ability to perform insertions and lookups in constant time, O(1), as opposed to other table types, which may require linear searches. Therefore, having the complete key facilitates this fast access pattern, making hashed tables ideal for situations where you have a specific identifier for the data you need to retrieve.

In contrast, scenarios where multiple records are read without key constraints, there are frequent writes but rare reads, or records are accessed based on non-key fields would not utilize the benefits of hashed tables effectively, as these scenarios would either not involve direct key access or would require more complex handling that is better suited to different table types, such as sorted or standard tables.