Clock page replacement policy vs LRU page replacement policy, is Clock more efficient?
If I understand correctly I think you are confusing the cache and the cache hit data structure. The structure isn't used to access the page, its used to store the hit count. For LRU, the OS needs to examine the hit count for every page in the cache memory to find the least recently used. When a page is hit, it is moved up in the list to prevent it from being evicted. I don't see how this would translate to a hash map.

The clock algorithm, only keeps track of a set of the most recently used pages (typically since the time since a new page was requested). The clock algorithm acts as an approximation of LRU without the maintenance of the linked list.