[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; 
    }
}