We use cookies (including Google cookies) to personalize ads and analyze traffic. By continuing to use our site, you accept our Privacy Policy.

SimplyLeet
TagsCompaniesDisclaimersPrivacyTermsContactAbout Us

A Number After a Double Reversal

Number: 2238

Difficulty: Easy

Paid? No

Companies: N/A

Problem Description

Given a non-negative integer num, reverse its digits to get reversed1, then reverse reversed1 to get reversed2. The goal is to determine whether reversed2 is equal to the original num. For example, if num is 526, reversing gives 625 and reversing again gives 526, which is equal to the original num.

Key Insights

  • Reversing an integer involves converting it to a string, reversing the string, and converting back to an integer (which removes leading zeros).
  • The double reversal property should normally return the original number, except for cases where trailing zeros in the original cause the first reversed value to lose those zeros.
  • Handling zero is trivial since reversing 0 yields 0.
  • The problem can typically be solved in O(d) time where d is the number of digits.

Space and Time Complexity

Time Complexity: O(d), where d is the number of digits in the number. Space Complexity: O(d), for the string representation of the number.

Solution

We solve the problem by performing the following steps:

  1. Convert the number to a string and reverse it to obtain reversed1.
  2. Convert reversed1 back to an integer (automatically dropping any leading zeros).
  3. Convert this integer back to a string, reverse it, and convert again to an integer to obtain reversed2.
  4. Compare reversed2 with the original number. The main trick here is to understand that converting the string back to an integer will remove any leading zeros resulting from the reversal process, which is the cause of discrepancies when the number contains trailing zeros.

We use simple string manipulation (reversal) and integer conversion. No advanced data structures or algorithms are needed for this problem.

Code Solutions

# Function to check if the double reversal equals the original number
def is_same_after_double_reversal(num):
    # Reverse the integer by converting it to a string, then reversing and converting back to int
    reversed1 = int(str(num)[::-1])
    # Reverse reversed1 similarly
    reversed2 = int(str(reversed1)[::-1])
    # Compare and return whether reversed2 is equal to the original num
    return reversed2 == num

# Example usage
num = 526
print(is_same_after_double_reversal(num))  # Output: True
← Back to All Questions