Palindrome Number – Leetcode #9

Problem Statement

This problem is from Leetcode – Palindrome Number. The problem statement is as below:

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

SOLUTION

In this question we are given an integer. We need to check if its a palindrome or not.

Approach

1. First we need to extract the individual digits out of the input integer and store in an ArrayList.
2. While input > 0 compute the modulus and store in the list. Further divide input by 10.
3. Covert the ArrayList into an integer array. This contains the individual digits of the given input.
4. Now in a for loop check if the first and last digits are the same. Break at the middle index.
5. Time complexity of this approach is O(n).

Lets see the code below:

Palindrome.java
public class PalindromeNumber {

	public static void main(String[] args) {
		

		PalindromeNumber pn = new PalindromeNumber();
		boolean isPalin = pn.isPalindrome(12321);
		
		System.out.println("Panlindrome: " + isPalin);
	}
	
        public boolean isPalindrome(int x) {
    	
    	    int num = x;
    	    boolean isPalin = true;

       
      //   if the given input is negative then return false 
    	    if(x < 0) {
    		
    		isPalin = false;
    	    }
    		
    	    List<Integer> numList = new ArrayList<>();
    
      /*   using this while loop extract the digits from the input and push 
       *   into an ArrayList

       */
     	    while (num > 0) {
	 		
     		System.out.println ( num % 10);
     		numList.add( num % 10);
	 		num = num / 10;

	 	} // end while
    	


      //    convert the ArrayList into an array
     	    Integer[] numArray = numList.toArray(new Integer[numList.size()]); 
     	    int len = numArray.length-1;


      /*    compare the first digit with the last digit. 
       *    Break out of the loop at middle index
       */
     	    for(int i=0; i<numArray.length; i++) {
     		
    
     		if(i == (len-i)) {
     			break;
     		}
     		else if(numArray[i] != numArray[len-i]) {
     			
     			isPalin = false;
     		}
     	    } // end for
     	
     	
    	return isPalin;

    } // end function

}  // end class

This code returns the output as below:

Panlindrome: true