9. Palindrome Number

Solved

Easy

Topics

Companies

Hint

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?

class Solution {

    /** T : O(n) S : O(1)   (do not convert it to sting )*/
    public boolean _isPalindrome(int x) {
        String str= x+"";
        int i=0, j= str.length()-1;

         while ( i< j){
                if( str.charAt(i++) != str.charAt(j--))
                    return false;
         }

         return true;
    }


    /**. T : O( n * ln(n) )  S: O(num(dig in x))  */
    public boolean __isPalindrome( int x){
        if( x<0) return false;
        
        List<Integer> digList=  findDigits( x, new ArrayList<>()) ;
        int i= 0, j= digList.size()-1;

        while( i< j){   
            if( digList.get(i++) != digList.get( j--)) return false;
        }
        return true;
    }

    public List<Integer> findDigits(int x, List<Integer> digList){
            while( x>0){
                digList.add( x%10);
                x/=10;
            }
            return digList;
    }

    /**. T : O( n * ln(n) )  S: O(num(dig in x))  */
    public  boolean isPalindrome( int x){

        return reverseIntegerX(x)== x;
    }

    public int reverseIntegerX( int x){
          int reverse=0;
          while( x>0){
                reverse= reverse*10 +  x%10;
                x/=10;
            }
        return reverse;
    }
}

/**

9. Palindrome Number
Solved
Easy
Topics
Companies
Hint
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?
 */

Explanation:

converting to the string , and using the pointers to check weather the

finding the reverse number involved in exceeding the inter limit