LeetCode刷题实战9：求解回文数

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

https://leetcode-cn.com/problems/palindrome-number

class Solution {  
public:
    bool isPalindrome(int x) {
        if (x<0)
            return false;
        long long int sum =0;
        long long int origin = x;
        while(x)
        {
            int num = x %10;
            sum = sum*10 + num;
            x/=10;
        }
        if(sum == origin)
            return true;
        else  
            return false;
    }
};

class Solution {
public:
    bool isPalindrome(int x) {
        // 负数肯定不是，以及首尾不对称的非0数
        if(x < 0 || (x % 10 == 0 && x != 0))
            return false;

        int rev = 0;
        while ( x > rev){
            rev = rev * 10 + x % 10; //将低位一半的数取反。
            x = int (x / 10);
        }
        //有rev >= x， 奇数情况下需要除去10
        return x == rev || x == int(rev/10);
    }
};

bool isPalindrome(int x) {
  if (x < 0) return false;
  int div = 1;
  while (x / div >= 10) {
    div *= 10;
  }
  while (x != 0) {
    int l = x / div;
    int r = x % 10;
    if (l != r) return false;
    x = (x % div) / 10; //去掉两边的数
    div /= 100;
  }
  return true;
}