Reversing a Number using Recursion in Python
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
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
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
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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))
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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