What is the number of swaps required to sort n elements using selection sort, in the worst case?
The site i am referring says theta(n).
Shouldnt it be theta(n2), cuz worst case it requires n swaps for each of the n elements.
Not for each element (which is what you stated previously). Selection sort requires at most n-1 swaps total because a swap is only performed after selecting the item to move (or not move, depending on the intermediate relative order). Thus, the worst case for swaps is indeed theta(n).