The efficiency of a variation of sequential search that counts the number of occurrences of a given search key in a list can be different from the classic sequential search, depending on how it's implemented. Let's consider both cases:

1. Classic Sequential Search:

   • In classic sequential search, you iterate through the list from the beginning to the end, checking each element to see if it matches the search key.
   • The time complexity of classic sequential search is O(n), where n is the number of elements in the list.
   • In this case, you don't count the number of occurrences; you stop when you find the first occurrence of the search key.

2. Variation with Counting:

   • In the variation that counts the number of occurrences, you continue scanning the entire list even after finding the first occurrence of the search key. You increment a counter each time you encounter a matching element.
   • The time complexity of this variation is still O(n) in the worst case because you may need to examine all elements in the list.
   • However, the efficiency differs in terms of the additional work required to count occurrences. While the time complexity is the same, the constant factors may differ. In other words, the variation that counts occurrences might take slightly more time due to the extra counting steps.

So, in terms of big O notation, both classic sequential search and the variation with counting have the same efficiency (O(n)). However, the actual execution time may vary slightly depending on how the counting is implemented, and it will generally take more time than the classic search since it performs additional operations.