[LeetCode#9] Palindrome Number

The questions: 

Determine whether an integer is a palindrome. Do this without extra space.

Analysis: 

To determine whether an integer is a palindrome, we could try following ways:

1. reverse the num into num', test iff num == num'.  (This method may encounter complex overlfow handle)

2. use two pointer : front and end. Compare the digit at front and end, then move on !

Skill:

1. chop off the first digit, use '%'

e: num = 65321,  num' = num % 10000=65321 % 10000 = 5321, then the first digit was chopped off

 

2. chop off the last digit, use '/'

e: num = 65321,  num' = num / 10 = 6532, then the last digit was chopped off

Note: it's different from we want to get the first digit and last digit.

1. get the first digit, use "/"

e: num = 65321,  digit = num / 10000=65321 / 10000 = 6

2. get the last digit, use "%"

e: num = 65321,  num' = num % 10 = 2

 

My solution: 

public class Solution {

    public boolean isPalindrome(int x) {

        

          if (x < 0)

            return false; 

            

        int front_digit = 0;

        int end_digit = 0;

        int remain_number = x; 

        int number_size = number_digit_size(x);

        int digit_left = number_size;

  

        while (digit_left > 1) {

            

            front_digit = remain_number / power_of_ten(digit_left - 1);

            end_digit = remain_number % 10;

            

            if (front_digit != end_digit) {

                return false; 

            }

            remain_number = remain_number % power_of_ten(digit_left - 1);//chop the first digit of the number

            remain_number = remain_number / 10; //chop the last digit of the number 

            

            digit_left = digit_left - 2;

        }

        

        return true;

    }



    static int power_of_ten(int count) {

        //return 10 ^ count

        int ret = 1;

        do {

            ret = ret * 10;

            count --; 

        } while (count > 0);

    

        return ret;

    }



    static int number_digit_size(int number) {

        //get the size of digits in the number

        int size = 0;

        if (number == 0)

        {

            return 1;

        }

    

        while (number != 0)

        {

            number = number / 10;

            size ++; 

        }

    

        return size; 

    }

}