In this post, you will learn how to reverse a list using recursion in python with a detailed explanation and algorithm.
To reverse a list using recursion we use a two-pointer approach. In this approach, we take two pointers L & R initially L point to the first element of the list and R points to the last element of the list.
Let’s understand whole concepts with the help of an example.
Take one list
L1 = [3,1,5,4,7] where initially L points to the first element of the list and R points to the last element of the list as shown below.
First swap the element at L with the element at R after that increment L (
L += 1) & decrement R (
R -= 1).
repeat the above step ( first swap the element at L with the element at R after that increment L & decrement R).
L >= R that means we have completed the task to reverse a list.
Here in this case
L == R means the list is reversed.
reverse of the list
l1 = [7,4,5,1,3].
Algorithm to Reverse a list using recursion
- Take two-pointers L & R.
- L point to the first element of the list and R point to the last element of the list.
L >= Rthen returns your list (
- otherwise, swap
- At the end return recursive function
Now we have understood how to write a program to reverse a list using recursion through the above algorithm.
But before we write a program few concepts you have to know:
- function in python &
- How recursive function work
def reverse_list(my_list, l, r): if l >= r: return my_list #swap tem = my_list[l] my_list[l] = my_list[r] my_list[r] = tem return reverse_list(my_list,l+1,r-1) my_l = [3,1,5,4,7] L = 0 R = len(my_l)-1 print('my list:',my_l) print('reverse list :',reverse_list(my_l,L,R))
my list: [3, 1, 5, 4, 7] reverse list : [7, 4, 5, 1, 3]
Fun Fact: In python, it is very simple to reverse a list, you just use slicing and step argument to reverse a list (
But for recursion, these are general steps you have to follow.