Reversing a Number using Recursion in Python

October 12, 2022

Reversing a Number using Recursion

On this page will learn to create Python Program for Reversing a Number using Recursion as well as loop.

Note : That the given program doesn’t consider leading zeroes. For example, for 100 program will print 1. If you want to print 001 then remove the int from print statement.

Example :

  • Input : 12345
  • Output : 54321
  • Explanation : Reverse of 12345 is 54321
Reverse Number in Python

Method 1 : Using Recursion

Algorithm

  • Start by converting number to list named as arr and passing the list, half of length of arr to a function
  • As value of n is not passed to function so it is set by default to 0
  • If n is equals to l return arr
  • Swipe the values of arr[n] and arr[-1*(n+1)]
  • Return the value of recursive call for same function with values passed arr, l, n+1
  • Convert the returned list to integer and Print
Python Program to Reversing a Number
To Learn more about Recursion   click here

Python Code

Run 
def reverse_digit(arr, l, n=0):
    if n == l:
        return arr
    arr[n], arr[-1*(n+1)] = arr[-1*(n+1)], arr[n]
    return reverse_digit(arr, l, n + 1)


num = 12345
arr = list(str(num))
arr = reverse_digit(arr, len(arr)//2)
s = ""
print(int(s.join(arr)))
Output :

Reverse of 12345 is 54321

Method 2 : Using Loop

Algorithm

  • Start by converting number to list named as arr and passing the list, half of length of arr to a function
  • Iterate from range 0 to l using variable i
  • Swipe the value of arr[i] and arr[-1*(i+1)]
  • Return arr
  • Convert the returned list to integer and Print

Python Code

Run 
def reverse_digit(arr, l):
    for i in range(l):
        arr[i], arr[-1 * (i + 1)] = arr[-1 * (i + 1)], arr[i]
    return arr


num = 12345
arr = list(str(num))
arr = reverse_digit(arr, len(arr)//2)
s = ""
print(int(s.join(arr)))
Output :

Reverse of 12345 is 54321
 
 

Smallest element in an array

Prime Number

Largest element in an array

Prime Course Trailer

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3 comments on “Reversing a Number using Recursion in Python”


  • Yash

    num=102
    l=len(str(num))

    def rev(num,l,out=0):
    if l==1:
    out=out+num
    return out
    else:
    rem=num%10
    out=out+(rem*(10**(l-1)))
    num=num//10
    print(out,num)
    return rev(num,len(str(num)),out)
    print(rev(num,l))

    1

  • ushaveeramallu901

    def rev(num,i):
    rem=num//pow(10,i-1)
    if num==0:
    return 0
    else:
    return rem +rev(num%pow(10,i-1),i-1)*10
    num=1002
    print(rev(num,len(str(num))))#2001

    0