The list method reverse reverses the elements in the list. define a function named reverse that reverses the elements in its list argument (without using the method try to make this function as efficient as possible, and state its computational complexity using big-o notation.

#code in python.

#function that reverse the element of list

def reverse(inp_lst):

   for i in range(len(inp_lst)//2):

       inp_lst[i], inp_lst[len(inp_lst) - i - 1] =inp_lst[len(inp_lst) - i - 1], inp_lst[i]

#main method

def main():

   #create a list

   lst1 = list(range(8))

   print("list before revere:",lst1)

   #call the method with list parameter

   reverse(lst1)

   print("list after revere:",lst1)

   #create another list

   lst2 = list(range(5))

   print("list before revere:",lst2)

   #call the method with list parameter

   reverse(lst2)

   print("list after revere:",lst2)

#call the main method    

main()

Explanation:

In main method, create a list and call the method revers() with the list parameter. In the revers() method, swap the first element with last and second with second last. Similarly loop will run half the length of list.This will reverse the elements of  the list.Then print the list before and after the revers in the main .Similarly  we can test it for another list.

As the loop run for n/2 time in the method reverse(), so the complexity of the code is O(n).

Output:

list before revere: [0, 1, 2, 3, 4, 5, 6, 7]                                                                              

list after revere: [7, 6, 5, 4, 3, 2, 1, 0]                                                                                

list before revere: [0, 1, 2, 3, 4]                                                                                        

list after revere: [4, 3, 2, 1, 0]

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