0009_PalindromeNumber.cpp

// Problem 9: Palindrome Number
// https://leetcode.com/problems/palindrome-number/

#include  <cmath>
using namespace std;
class Solution {
public:
    bool isPalindrome(int x) {
        // 設置是否為回文的boolean, 頭尾數值的int, 和目前位數與最大基數
        bool palindromeOrNot = 0;
        int xFirst, xLast;
        int power = 0;
        int base;
        
        // 先計算總共幾位數
        int xCount = x;
        while (xCount != 0)
        {
            power++;
            xCount /= 10;
        }
        
        while (palindromeOrNot == 0){
            if (x < 0) break; // 如果已經把x檢查完, 就結束
            if (power < 2){ // 如果x只剩1位數且還在這(while迴圈目前判斷前後都相同), 視為回文並結束
                palindromeOrNot = 1;
                break;
            }
            
            // 更新基數, 取得頭尾
            base = pow(10, power - 1);
            xFirst = x / base;
            xLast = x % 10;
            
            // 比較頭尾數字
            if (xFirst != xLast) break;
            x = x % base - xLast;
            x /= 10;
            power -= 2;
        }
        return palindromeOrNot;
    }
};