9.palindrome-number.cpp

/*
 * @lc app=leetcode id=9 lang=cpp
 *
 * [9] Palindrome Number
 *
 * https://leetcode.com/problems/palindrome-number/description/
 *
 * algorithms
 * Easy (41.96%)
 * Total Accepted:    513.6K
 * Total Submissions: 1.2M
 * Testcase Example:  '121'
 *
 * Determine whether an integer is a palindrome. An integer is a palindrome
 * when it reads the same backward as forward.
 *
 * Example 1:
 *
 *
 * Input: 121
 * Output: true
 *
 *
 * Example 2:
 *
 *
 * Input: -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: 10
 * Output: false
 * Explanation: Reads 01 from right to left. Therefore it is not a
 * palindrome.
 *
 *
 * Follow up:
 *
 * Coud you solve it without converting the integer to a string?
 *
 */
#include <math.h>
#include <iostream>
class Solution {
   public:
    bool isPalindrome(int x) {
        if (x < 0 || (x > 10 && x % 10 == 0)) {
            return false;
        }
        int a = 1;
        int b = x;
        while (b / 10) {
            b /= 10;
            a *= 10;
        }
        b = x;
        int top;
        while (b) {
            top = b / a;
            if (top != b % 10) {
                return false;
            }
            b %= a;
            b /= 10;
            a /= 100;
        }

        return true;
    }
};