9. Palindrome Number

題目原文

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:

Could you solve it without converting the integer to a string?

解題思路

1. 每次先計算% ，取得最低位，每次迭代*10變成reverse的最高位。

2. 最後比較兩數是否相等。

3. 負數必為False。

程式解答

class Solution 
{
public:
    bool isPalindrome(int x) 
    {
        int j = x;
        int i = 0;
        int rev = 0;
        
        if (x < 0)
            return false;
        while (x)
        {
            rev *= 10;
            i = x;
            i %= 10;
            rev += i;
            x /= 10;
        }
        if (j == rev)
            return true;
        return false;
    }
};