491. Palindrome Number【easy】

Check a positive number is a palindrome or not.

A palindrome number is that if you reverse the whole number you will get exactly the same number.

Notice

It's guaranteed the input number is a 32-bit integer, but after reversion, the number may exceed the 32-bit integer.

 

Example

11, 121, 1, 12321 are palindrome numbers.

23, 32, 1232 are not palindrome numbers.

解法一：

 class Solution {
 public:
     /*
      * @param num: a positive number
      * @return: true if it's a palindrome or false
      */
     bool isPalindrome(int num) {
         //negative number
         if(num < )
             return false;

         int len = ;
         while(num / len >= )
             len *= ;

         while(num > )    {

             //get the head and tail number
             int left = num / len;
             int right = num % ;

             if(left != right)
                 return false;
             else    {
                 //remove the head and tail number
                 num = (num % len) / ;
                 len /= ;
             }
         }

         return true;
     }
 };

分别过滤出头尾2个数进行比较

解法二：

 class Solution {
 public:
     /*
      * @param num: a positive number
      * @return: true if it's a palindrome or false
      */
     bool isPalindrome(int num) {
         if (num < )
             return false;  

         if (num < )
             return true;  

         int digits = ;
         int t = num;
         int d = ;
         while(t != ) t /= , ++d;  

         int left = pow(, d - );
         int right = ;
         while( left >= right)
         {
             if (num / left %  != num / right % )
                 return false;  

             left /= ;
             right *= ;
         }
         return true;
     }
 };

依旧是过滤出头尾2个数进行比较，处理的方式和解法一稍有不同，参考@MagiSu 的代码