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leetcode 009: palindrome number

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

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problem:

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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:

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

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start code (c++)

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class Solution {
public:
    bool isPalindrome(int x) {
        
    }
};

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solution 1:

我的思路：
很容易想到的是，比如对于 123456,我们可以很方便从右到左取出每一位数字，6 5 4 3 2 1，然后生成一个新的数字 654321， 比较 654321 与 123456 是否相等。 但是这里要注意到一个问题，int 的大小是有限制的，你在生成 654321 的时候，有可能会产生溢出。 我这里的思路是，对于 123456，我们首先去除 最右边的 6，同时去除最左边的 1，然后采用 1 == 6 && 2345 == 5432 来比较， 这样由于我们比原来的数至少缩小了 100 倍，肯定不会溢出的。

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class Solution {
public:
    bool isPalindrome(int x) {
        if (x < 0)
            return false;
        if (x < 10)
            return true;

        // for example x = 12345,
        // finally, rightDigit = 5, 
        // x = 1,
        // x1 = 234,
        // x2 = 432
        int rightDigit = x % 10;
        x = x / 10;
        int x2 = 0;
        int x1 = 0;
        int base = 1;
        while (x > 9){
            int digit = x % 10;
            x = x / 10;
            x2 = x2 * 10 + digit;
            x1 = x1 + digit * base;
            base *= 10;
        }
        return x == rightDigit && x1 == x2;
    }
};

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