Leetcode 9: Palindrome Number

Category : Easy

Problem

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

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

https://leetcode.com/problems/palindrome-number/

Examples

Example 1:

Input: x = 121
Output: true

1 2	Input: x = 121 Output: true

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.

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.

Input: x = 10

Output: false

Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Example 4:

Input: x = -101
Output: false

1 2	Input: x = -101 Output: false

Constraints

-2³¹ <= x <= 2³¹ - 1

Solution Approach

To check if the number is palindrome or not we just reverse the number by taking out the last digit from the number one by one and concatenating those digits to a new reverse number. In the end, we will compare those two numbers (original and the concatenated reverse number) and if they are equal then we can say that the number is palindrome otherwise they are not.

Solution code

class Solution {
  public boolean isPalindrome(int x) {
      int num = x, rev = 0;
      if(x<0)
          return false;
      while(x!=0){
          int d = x%10;
          x = x/10;
          rev = rev*10 + d;
      }
      return (rev==num);
    }
}

class Solution {

public boolean isPalindrome(int x) {

int num = x, rev = 0;

if(x<0)

return false;

while(x!=0){

int d = x%10;

x = x/10;

rev = rev*10 + d;

}

return (rev==num);

}

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