Question

this a part of code for Quick Sort algorithm but realy I do not know that why it uses rand() %n please help me thanks

Swap(V,0,rand() %n)  // move pivot elem to V[0]

Answer 1

It is used for randomizing the Quick Sort to achieve an average of nlgn time complexity.

To Quote from Wikipedia:

What makes random pivots a good choice?

Suppose we sort the list and then
divide it into four parts. The two
parts in the middle will contain the
best pivots; each of them is larger
than at least 25% of the elements and
smaller than at least 25% of the
elements. If we could consistently
choose an element from these two
middle parts, we would only have to
split the list at most 2log2n times
before reaching lists of size 1,
yielding an algorithm.