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 < 0)
            return false;
            
        int len = 1;
        while(num / len >= 10)
            len *= 10;
            
        while(num > 0)    {
            
            //get the head and tail number
            int left = num / len;
            int right = num % 10;
            
            if(left != right)
                return false;
            else    {
                //remove the head and tail number
                num = (num % len) / 10;
                len /= 100;
            }
        }
        
        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 < 0)  
            return false;  
              
        if (num < 10)  
            return true;  
              
        int digits = 0;  
        int t = num;  
        int d = 0;  
        while(t != 0) t /= 10, ++d;  
          
        int left = pow(10, d - 1);  
        int right = 1;  
        while( left >= right)  
        {  
            if (num / left % 10 != num / right % 10)  
                return false;  
              
            left /= 10;  
            right *= 10;  
        }  
        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