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Palindrome Number: Leetcode Problem #9

Originally published at

Understanding Problem

As per the problem we have been given an integer and we need to check if it is palindromic or not.

input_x    = 121
reversed_x = 121
input_x and reversed_x are palindromic
input_x = -121
reversed_x = 121-
input_x and reversed_x are not palindrominc

My Thought About Solution

  • The solution looks pretty easy for me, we just have to read input integer digits backward and construct reversed integers.
  • Then we can compare the input integer and reversed integer and return the result.
  • One additional optimization we can do is that we can return negative integers without even checking if its palindromic or not since negative signs will make them not palindromic.
  • Data structure: We are not using any collection, just integer is enough to hold the data.
    Time-complexity: O(length(N)) where N is the input integer
    Space-complexity: O(1) constant space


1: First check if input integer is negative , if yes the return false , since input integers cannon be palindromic due do - sign
2: Construct reversed input integer by reading from last digit and append to reversed integer
3: Now compare the input integers and return the result



Our Code Runtime beats 99.96% of the submission. Nice job!


This Leetcode is a good problem to understand

  • How to iterate over each digit in integer and play around with it.
  • Optimizing solution by finding out cases where we don't need to perform our core business logic.

Let me know if you have some opinion on the solution in the comment!

Happy Leetcoding!

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