Is Palindrome Number easy or hard?

Palindrome Number is classified as an Easy problem. The string-based solution is straightforward, but the constant-space mathematical approach introduces useful concepts like digit extraction and partial number reversal.

Palindrome Number Python/Java solution

In Python or Java, you can either convert the integer to a string and check if it equals its reverse, or implement the mathematical approach that reverses half of the digits using modulo and division. The math approach is typically preferred in interviews because it runs in O(log n) time and constant space.

How to solve Palindrome Number in O(log n)?

Repeatedly remove the last digit of the number using x % 10 and append it to a reversed variable using reversed = reversed * 10 + digit. Stop when the reversed value becomes greater than or equal to the remaining number. If both halves match (or match after removing the middle digit for odd lengths), the number is a palindrome.

What is the best approach for Palindrome Number?

The most efficient approach reverses only half of the digits using integer arithmetic. Extract digits with modulo and build a reversed half until it matches the remaining half. This method runs in O(log n) time and uses O(1) space because it avoids converting the number to a string.

Is Palindrome Number asked at Google/Amazon/Meta?

Palindrome Number is a common screening problem across major tech companies. Variations of digit reversal and palindrome checks appear in interview preparation sets used by Google, Amazon, Meta, and Microsoft to test basic algorithmic thinking and edge case handling.

What data structure is used in Palindrome Number?

The optimal solution uses no additional data structures and works directly with integer arithmetic. The simpler implementation converts the number to a string and compares characters from both ends using a two-pointer style comparison.

What is the time complexity of Palindrome Number?

The optimal solution runs in O(log n) time because the algorithm processes each digit once. Since the number of digits in an integer grows logarithmically with its value, reversing half the digits requires proportional work.

Description Hints 1 Solution Video 12:00

9. Palindrome Number

Easy61.0% acceptance31 companies

Given an integer x, return true if x is a palindrome, and false otherwise.

Example 1:

Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

Input: x = -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Constraints:

-2³¹ <= x <= 2³¹ - 1

Follow up: Could you solve it without converting the integer to a string?

Asked at top 20 of 31 companies

Meta Cognizant Bcg

EXL Luxoft

Infosys Accenture Qualcomm Garmin Mindtree

Google Amazon

+8 more

Microsoft Bloomberg

TCS Yandex SAP Yahoo AMD LTIMindtree

Topics

Math

Hints open one at a time

Hint 1

Beware of overflow when you reverse the integer.

12:00

Still stuck?Read 3 approaches, or watch a walkthrough.

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