def mergeSort(lst: list) -> list:
    if len(lst) > 1:
        mid = len(lst) // 2
        left = lst[:mid]
        right = lst[mid:]

        mergeSort(left)
        mergeSort(right)

        i = j = k = 0

        while i < len(left) and j < len(right):
            if left[i] <= right[j]:
                lst[k] = left[i]
                i += 1
            else:
                lst[k] = right[j]
            

print(mergeSort([3,5,2,1]))