9. Palindrome Number 验证回文数字

Determine whether an integer is a palindrome. Do this without extra space.

Some hints: Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem “Reverse Integer”, you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

Difficulty: Easy

  • 需求是不允许使用额外的空间
  • 负数不是回文数字
  • 可以比较首尾数字是否相同比较
class Solution {
public:
    bool isPalindrome(int x) {
        if (x<0) return false;
        int div = 1;
        while (x / div >= 10) div *= 10;
        while (x > 0)
        {
            int left = x / div;
            int right = x % 10;
            if (left != right) return false;
            //更新x
            x = (x % div) / 10;
            //更新div
            div /= 100;
        }
        //如果为0的话
        return true;
    }
};
 
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