LeetCode习题笔记——判断数字是否回文

直接上题：

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

这个题最大的要求就是不能用额外空间，即不可以将数字转为字符串然后再用判断字符串回文的方式。然而还是比较简单的：class Solution {
public:
bool isPalindrome(int x) {
int a = x, r = 0;

if (x < 0) return false;

while (a > 0) {
r = r*10 + a%10;
a = a / 10;
}

return r == x;
}
};

相当于一直将数字第一个数位作为比较数的末尾，最后看得到的数字是否相同即可。