A well know algorithm that uses a divide and conquer strategy is the mergesort algorithm. $($a$)$ Given that a procedure mergelist $($list$,$ first,middle,middle$+1,$last$)$ already exists for combining two lists together in sorted order write the top level pseudocode for the mergesortalgorithm.

list is and array of n items to be sorted from index locations first to last,

$($b$)$ Explain in detail how mergelist from part $($a$)$ works. Indicate in your explanation why in a worst case scenario n$-1$ comparisons would be required for a list of n elements. This is the DSA question. Please provide the right answers for $($b$).$