Recursive Mergesort

B[1..n] is an auxiliary array;

Mergesort(i,j) {sorts the subarray A[i,j] }

if i < j then

k := (i+j)/2;

Mergesort(i,k);

Mergesort(k+1,j);

Merge A[i..k] with A[k+1..j] into B[i..j];

Copy B[i..j] into A[i..j];