merge sort

Question

Consider the following variation on merge sort for the large values of 'n  'instead of recursing until 'n' is sufficiently small recur atmost a constant 'r' times and then use insertion sort to solve the 2^r resulting sub problems.What is the running time of this variation

a)theta(n)

b)theta(n log n)

c)theta(n²)

d)theta(log n)

Comments

Answer should be theta (n logn). I don't know how, but I read it once somewhere. And this is the way sort function is implemented in STL of C++

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its given as theta (n²)

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sorry I was wrong.

This may help you: https://gateoverflow.in/99455/sorting-algorithm

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its not clear from that link

Can someone please help

@habib @arjun sir