Divide & conquer sorting algorithms:

algorithm         size of pieces          strategy 

insertion sort     1 & n-1       sort piece of size n-1             
                                 insert piece of size 1

selection sort     1 & n-1       find min, move it left
                                    (it's the piece of size 1)
                                 sort piece of size n-1

mergesort          n/2 & n/2     sort pieces of size n/2
                                 merge the sorted pieces

quicksort           n/2 & n/2     move small elements left
                    (ideally)        and large elements right
                                  sort the small & large elements