Create a Python program to reverse a number in Python.
This article will show multiple solutions for reversing a number in Python.
Reversing a number mathematically
The algorithm below is used to reverse a number mathematically with time complexity of O(log n) where n is input number.
rev_num = 0
(2) Loop while
num > 0
- (a) Multiply
rev_numby 10 and add remainder of num divide by 10 to
- (b) Divide num by 10
num = 12345 rev_num = 0 while num != 0: rev_num = rev_num * 10 rev_num = rev_num + (num%10) num = num // 10 print(rev_num)
Using reversed() method
Python’s built in
reversed() method returns an iterator that accesses the given sequence in the reverse order.
# input num = 1234 rev_iterator = reversed(str(num)) rev_num = "".join(rev_iterator) print(rev_num)
Note that the
reversed() method doesn’t accept integer as a parameter therefore data type is converted to a string.
reversed() returns an iterator we need to join it before printing it out.
Python string supports slicing to create substring.
The slicing starts with the
start_pos index (included) and ends at the
end_pos index (excluded). The step parameter is used to specify the steps to take from the start to end index.
num = 123 rev_num = str(num)[::-1] print(rev_num)
Since slicing work on a string we need to convert the number to a string, then create a slice that starts with the length of the string, and ends at index 0 with a step of -1.